JUDGMENT : G.R. SWAMINATHAN, J. 1. This writ appeal is directed against the order dated 16.04.2018 allowing W.P. (MD) No. 15733 of 2014 filed by the respondents herein. 2. The respondents are working as vocational instructors in government higher secondary schools. They were placed in pre-revised scale of pay of Rs. 1400-2600 and revised scale of pay of Rs. 5500-175-9000. According to them, this fixation was erroneous since vide G.O.Ms. No. 840 dated 31.07.1990, the time scale of pay for vocational instructors having B.Sc. (Agri) qualification was directed to be fixed as Rs. 2000-3500 (equivalent to Rs. 6500-11100). They represented to the government seeking pay scale parity. The request was rejected by the Director of School Education, Chennai vide proceedings in Na. Ka. No. 24069/VI/V3/2014, dated 21.08.2014. Challenging the same, they filed W.P. (MD) No. 17533 of 2014. They contended that the issue raised by them had already been answered in their favour in W.A. (MD) No. 1344 of 2013 dated 14.08.2014 (The State of Tamil Nadu represented by its Secretary, School Education Department, Chennai and two others Vs. Vasimalai and another). The learned single Judge accepted the said contention and allowed the writ petition. 3. Questioning the same, the State filed this writ appeal. Before the Division Bench, the Special Government Pleader submitted that the previous order on which reliance was placed by the learned single Judge was clearly distinguishable on facts. Though the Division Bench was inclined to sustain the said contention, it noted that another Division Bench vide order dated 21.01.2019 in W.A. (MD) No. 1040 of 2019 had also followed Vasimalai. The factual matrix in W.A. No. 1040 of 2019 was similar to the facts on hand. Hence the matter was referred to the Full Bench by framing the following question: "Is a Vocational Instructor recruited through Teachers Recruitment Board for the post created in G.O.Ms. No. 129 School Education (HS3) Department dated 18.05.1999 and G.O.Ms. No. 63, School Educational Department dated 13.03.2007 the scale of pay, having been prescribed in the ad hoc Rules issued in the G.O.Ms. No. 6, School Educational (VE) Department dated 04.01.2000, entitled to get higher salary on par with those who were appointed initially as double part time Vocational Instructors and brought under regular scale of pay subsequently but prior to the framing of ad hoc Rules?" 4. No. 6, School Educational (VE) Department dated 04.01.2000, entitled to get higher salary on par with those who were appointed initially as double part time Vocational Instructors and brought under regular scale of pay subsequently but prior to the framing of ad hoc Rules?" 4. Learned Special Government Pleader appearing for the appellants reiterated the contentions set out in the memorandum of grounds of appeal and prayed for setting aside the order of the learned single Judge and for allowing the writ appeal. 5. Per contra, learned Senior Counsel appearing for the respondents submitted that there is absolutely no merit in this appeal. According to him, the learned single Judge had correctly applied the principle of equal pay for equal work. When some of the vocational instructors (Agriculture) are in the pay scale of Rs. 6500-11100, the respondents, who are discharging the very same duties and functions, cannot be placed in a lesser scale of pay (Rs. 5500-9000). He drew our attention to the decisions of the Hon'ble Supreme Court reported in Randhir Singh vs. Union of India, (1982) 1 SCC 618 and State of Punjab and Others vs. Jagjit Singh and Others, (2017) 1 SCC 148 to drive home his point. 6. We have carefully considered the rival contentions and gone through the material on record. To appreciate the facts of the case, it is necessary to briefly consider the historical background. 7. The Education Department of the government of Tamil Nadu introduced the higher secondary/plus-two system in 1978-79. It also permitted starting of vocational courses in higher secondary schools vide G.O.Ms. No. 1719, dated 14.09.1978. Vocational courses were started in 709 out of 874 higher secondary schools. The total number of courses was 1153. The major vocational groups under which the 1153 courses fell were as follows: Agriculture 145 Home Science 110 Commerce and Science 474 Engineering and Technology 352 Health 68 Miscellaneous 4 Total 1153 8. In fact, vocational courses were in existence even earlier. For 491 out of 1153 courses, staff were also available. For the remaining vocational courses, it was proposed to draft vocational instructors on part-time basis. Depending on the situational requirements, persons were also appointed as double part-time vocational instructors. BSc., (Agri) was the prescribed qualification for vocational instructor (Agri). The part-time posts carried a consolidated remuneration. For 491 out of 1153 courses, staff were also available. For the remaining vocational courses, it was proposed to draft vocational instructors on part-time basis. Depending on the situational requirements, persons were also appointed as double part-time vocational instructors. BSc., (Agri) was the prescribed qualification for vocational instructor (Agri). The part-time posts carried a consolidated remuneration. Later, representations were received for regularisation of their services and for fixing reasonable time scale of pay. There were 1837 double part-time vocational instructors working in the higher secondary schools. The government decided to regularise their services over a period of two years from 1990-1991 onwards. To this effect, G.O.Ms. No. 712 dated 28.05.1990 was issued creating 800 posts of vocational instructors in the scale of pay of Rs. 1400-2600. The government also appointed a One-Man Committee to review the entire concept of vocationalisation in higher secondary schools and to undertake a data-based study regarding their regularisation. It also amended the schedule to the Tamil Nadu Revised Scale of Pay Rules, 1989 placing agricultural instructors having BSc. (Agri) degree in the time scale of pay of Rs. 2000-3500 vide G.O.Ms. No. 840, Finance Department dated 31.07.1990. During the relevant time, vocational instructors fell under two broad classes. The first was vocational instructors working in the government schools even prior to the introduction of the plus-two system (higher secondary course). The second was the part-time vocational instructors, who were categorised into four sub-classes namely, (a) fully qualified double part-time teachers (b) unqualified double part-time teachers (c) qualified single part-time teachers and (d) unqualified single part-time teachers. G.O.Ms. No. 967, dated 16.10.1992 was issued to deal with various categories of part-time vocational instructors. 587 fully qualified double part-time teachers were brought into regular scale of pay. Unqualified 450 double part-time teachers were to be trained and absorbed in the regular scale of pay. All qualified single part-time teachers were to be absorbed in the existing sanctioned secondary grade posts. Other unqualified single part-time teachers were to be given training and absorbed as secondary grade teachers in future. Sanction was accorded for the creation of 587 posts of vocational instructors in the scale of pay of Rs. 1400-2600 so as to absorb the fully qualified double part-time teachers on regular basis with effect from 16.10.1992. It also ordered abolition of 587 double part-time teacher posts. 9. Sanction was accorded for the creation of 587 posts of vocational instructors in the scale of pay of Rs. 1400-2600 so as to absorb the fully qualified double part-time teachers on regular basis with effect from 16.10.1992. It also ordered abolition of 587 double part-time teacher posts. 9. The single part-time teachers who felt aggrieved by the aforesaid government orders challenged the same before the Tamil Nadu Administrative Tribunal. The Tribunal ordered that the government should re-examine and formulate a policy by giving due regard to seniority. Pursuant to the aforesaid direction, the issue was re-examined and G.O.Ms. No. 834, dated 23.09.1994 was issued. The government ordered the creation of 1387 posts of vocational instructors on regular time scale of pay of Rs. 1400-2600. These posts were to be filled up by the fully qualified part-time teachers according to their seniority irrespective of whether they were working as double or single part-time instructors. Several other directions were issued to deal with the four categories of vocational instructors mentioned above. 10. It has already been noted that there were vocational instructors working in the government schools even prior to the introduction of the plus-two system (higher secondary course). Those possessing BSc.,(Agri) qualification, were placed in the pay scale of Rs. 2000-3500 on par with post-graduate teachers following the implementation of G.O.Ms. No. 840, dated 31.07.1990. They were termed as bifurcated instructors. But the part-time vocational instructors who were regularised with effect from 16.10.1992 were in the pay scale of Rs. 1400-2000. Some of such regularised part-time vocational instructors filed W.P. No. 19224 of 1998 while one G. Narayanasamy filed O.A. No. 1755 of 1998 before the Administrative Tribunal seeking revision and enhancement of pay scale at par with the bifurcated instructors. Following the abolition of the Tribunal, O.A. No. 1755 of 1998 was transferred to the High Court and re-numbered as W.P. No. 32121 of 2006 (T). W.P. No. 19224 of 1998 filed by T. Elamathiyan and seven others was dismissed on 23.03.2009 on the ground that the demand has to be considered only by the government and it was not for the Court to interfere. W.P. No. 32121 of 2006 was listed before another Judge. The order dated 23.03.2009 made in W.P. No. 19224 of 2009 was not brought to the notice of the learned Judge. W.P. No. 32121 of 2006 was listed before another Judge. The order dated 23.03.2009 made in W.P. No. 19224 of 2009 was not brought to the notice of the learned Judge. W.P. No. 32121 of 2006 was allowed on the basis that there cannot be two sets of vocational instructors drawing different scales of pay while doing the same work. The act of the department in fixing lower scale of pay for the regularised double part-time vocational instructors was held to be discriminatory and violative of Article 14 r/w Article 39 (d) of the Constitution of India. 11. Questioning the said order, the government filed W.A. No. 1814 of 2011. In the meanwhile, one Selvakumar and four others filed W.P. No. 17801 of 2000 seeking similar relief. The learned Judge before whom the case was listed noticed the conflict between the two orders in W.P. No. 19224 of 1998 and W.P. No. 32121 of 2006. The matter was placed before the Division Bench, which dismissed the writ petition by holding that the view taken in G. Narayanasamy's case was not in accordance with law. Since such a finding foreclosed G. Narayanasamy's case in the pending writ appeal, he filed Rev. Appln. No. 2 of 2011. By order dated 11.02.2011 it was disposed of by deleting the aforesaid adverse observation. The Division Bench also recorded the submission of the Special Government Pleader that the factual and legal matrices obtaining in the aforesaid two writ petitions were different and that they had filed W.A. No. 1814 of 2011 without knowing the implications. W.A. No. 1814 of 2011 consequently suffered a dismissal. S.L.P.(Civil) No. 22874 of 2012 questioning the same was also dismissed on 01.07.2013. After G. Narayanasamy filed Cont. P. No. 1576 of 2012, the government implemented the judicial orders by issuing G.O. (1D) No. 327, School Education Department, dated 18.11.2013. 12. One Vasimalai who was also regularised with effect from 16.10.1992 like G. Narayanasamy filed W.P. (MD) No. 5766 of 2008. His writ petition was allowed on 05.03.2012. Questioning the same, the government filed W.A. (MD) No. 1344 of 2013. The Division Bench took the view that the issue involved was covered by G. Narayanasamy's case and dismissed the writ appeal on 14.08.2014. 13. Now the question that arises for consideration is whether the learned single Judge was justified in applying those decisions in the case of the respondents also? 14. The Division Bench took the view that the issue involved was covered by G. Narayanasamy's case and dismissed the writ appeal on 14.08.2014. 13. Now the question that arises for consideration is whether the learned single Judge was justified in applying those decisions in the case of the respondents also? 14. We are of the view that the respondents cannot compare themselves with the double part-time instructors who were regularised under G.O.Ms. No. 967, dated 16.07.1992. There is a line of control (LOC) running across and demarcating the present case from the previous ones. The government took a policy decision in the year 1999 to create 100 temporary posts of vocational instructors with basic pay of Rs. 5500-175-9000 to introduce the subject of agriculture in 100 schools. G.O.Ms. No. 129 dated 18.05.1999 was issued to that effect. It was termed as a new project. Budgetary allocation was to be made on that basis. Ad hoc rules for the said post of vocational instructors in higher secondary schools was issued in exercise of powers conferred by the proviso to Article 309 of the Constitution of India vide G.O.Ms. No. 6, dated 04.01.2000. The rules were deemed to have come into force on the 23rd day of September, 1994. Rule 8 of the said rules reads that the vocational instructors shall be paid a monthly pay calculated in the scale of pay specified in column (3) of sub rule 8. Rule 9 stated that nothing contained in the Ad hoc rules shall adversely affect any person holding the post on the date of issue of the rules. 15. According to rule 2, the posts shall constitute a separate category in separate class in the Tamil Nadu School Educational Subordinate Service. Direct recruitment was to be one of the modes of appointments. The joint director of school education (higher secondary) shall be the appointing authority. The respondents herein were selected in the recruitment process conducted by the Teachers Recruitment Board. S. Rajaram and M. Rajkumar were appointed on 25.09.2001. M. Gopalakrishnan was appointed on 13.01.2009. The proceedings issued by the appointing authority refer to G.O.Ms. No. 129, dated 18.05.1999. It is also mentioned that the appointees will be drawing pay in the scale of 5500-175-9000. 16. The legal position no longer admits of any doubt. Certain anomalies may arise in specific cases. M. Gopalakrishnan was appointed on 13.01.2009. The proceedings issued by the appointing authority refer to G.O.Ms. No. 129, dated 18.05.1999. It is also mentioned that the appointees will be drawing pay in the scale of 5500-175-9000. 16. The legal position no longer admits of any doubt. Certain anomalies may arise in specific cases. There cannot be perfect equality in any matter on an absolute scientific basis and there may be certain inequities here and there (Para 5 in H.P. Gupta and Another vs. Union of India, (2002) 10 SCC 658 ). Grant of the benefit of the doctrine of "equal pay for equal work" depends upon a large number of factors including equal work, equal value, source and manner of appointment, equal identity of group and wholesale or complete identity (Para 24 in State of Punjab vs. Surjit Singh and Others, (2009) 9 SCC 514 ). If this test of complete or wholesale identity is applied, the respondents have to necessarily fail. The respondents were recruited under a particular G.O. which created a separate class of posts with a specified pay scale governed by statutory Ad hoc rules. Both G. Narayansamy as well as Vasimalai were regularised before the coming into force of the Ad hoc rules. They were not recruited under G.O.Ms. No. 129 dated 18.05.1999. They do not belong to the class to which the respondents herein were appointed. It is true that the respondents are discharging the same duties and responsibilities discharged by G. Narayanasamy and Vasimalai. But that cannot be the sole criterion to determine the issue. A mathematical analogy may clarify better. G. Narayanasamy and Vasimalai constitute a 'set'. The respondents constitute another 'set'. If we super-impose one on the other, and a complete and wholesale identity obtains, then a case for parity is made out and not otherwise. Mere overlapping is not sufficient. In the present case there is only overlapping and no complete/wholesale identity. 17. A recent decision of the Hon'ble Supreme Court reported in State of Bihar and Others vs. Bihar Secondary Teachers' Struggle Committee, Munger and Others, AIR 2019 SCC 2521 which reviews of the earlier rulings including Randhir Singh and Jagjit Singh referred to by the learned Senior Counsel appearing for the respondents is more on the point. 17. A recent decision of the Hon'ble Supreme Court reported in State of Bihar and Others vs. Bihar Secondary Teachers' Struggle Committee, Munger and Others, AIR 2019 SCC 2521 which reviews of the earlier rulings including Randhir Singh and Jagjit Singh referred to by the learned Senior Counsel appearing for the respondents is more on the point. It holds that the doctrine of equal pay for equal work is not an abstract doctrine and that it has no mechanical application in every case. The applicability of the principle must be left to be evaluated and determined by an expert body. The grant of time scale of pay is purely an executive function and hence the Court should not interfere with the same. Grant of pay parity which the Court may grant may result in a cascading effect and reaction which can have adverse consequences. Before entertaining and accepting claims, based on the principle of equal pay for equal work, the Court must consider the factors like source and mode of recruitment/appointment. In a given case, mode of selection may be considered as one of the factors which may make a difference. It is quite possible that due to certain reasons there can emerge two classes with one being a dying or vanishing cadre. The service incidents of these two cadres will be different. That by itself would not be discriminatory. [Paragraphs 68, 76 and 77]. Adopting the very same reasoning, we note the vocational instructors employed in the higher secondary schools prior to the introduction of G.O.Ms. No. 129, dated 18.05.1999 can be said to constitute a vanishing cadre and therefore their service incidents can be different from those appointed subsequently under the said GO. 18. We still have to deal with the order dated 21.01.2019 made in W.A. No. 1040 of 2019 (The Government of Tamil Nadu Represented by its Principal Secretary, School Educational Department vs. Kalarani and Others). It is true that the case of the respondents therein is similar to that of the respondents herein. It also appears that the order dated 21.01.2019 in W.A. No. 1040 of 2019 had attained finality. Yet, we are of the view that the present writ appeal cannot be governed by the order dated 21.01.2019 for more than one reason. It is true that the case of the respondents therein is similar to that of the respondents herein. It also appears that the order dated 21.01.2019 in W.A. No. 1040 of 2019 had attained finality. Yet, we are of the view that the present writ appeal cannot be governed by the order dated 21.01.2019 for more than one reason. The Division Bench which dismissed W.A. No. 1040 of 2019 was under the impression that the vocational instructors (Agriculture) and vocational instructors in other streams though discharge identical duties, were placed in different time scales. It is not so. A mere look at G.O.Ms. No. 6 dated 04.01.2000 is enough to dispel the same. The vocational instructors whether for Home Science, Commerce and Business and Agricultural, Engineering and Technology, Health or Photography and Music have been placed in the very same time scale of pay of Rs. 5500-175-9000. Secondly, the Division Bench took the view that the decisions rendered in G. Narayansamy and Vasimalai should be followed. We have already held that vocational instructors appointed under G.O.Ms. No. 129, dated 18.05.1999 r/w G.O.Ms. No. 6, dated 04.01.2000 constitute a separate class distinct from the one to which G. Narayanasamy and Vasimalai belonged. 19. It is well settled that Article 14 of the Constitution of India cannot be invoked for perpetuating illegality. A wrong order passed in one case cannot be made the basis for compelling a public authority to pass similar order in any other case. Even if the State implements an erroneous order passed by the Court, it cannot be precluded from challenging a similar order passed in another case, simply because appeal was not preferred in the earlier case (Paragraph No. 17 in State of Madhya Pradesh vs. Ramesh Chandra Bajpai, (2009) 13 SCC 635 ). 20. To reiterate, vocational instructors recruited through the Teachers Recruitment Board for the posts created vide G.O.Ms. No. 129, dated 18.05.1999 and G.O.Ms. No. 63, dated 13.03.2007, who are governed by G.O.Ms. No. 6, dated 04.01.2000 are not entitled to claim parity of pay scale with those appointed initially as double part-time vocational instructors and who were subsequently regularised under G.O.Ms. No. 967, dated 16.10.1992. 21. The reference is answered accordingly. The order of the learned single Judge is set aside. W.A. (MD) No. 201 of 2021 is allowed. No costs. Consequently, C.M.P. (MD) No. 622 of 2021 is also dismissed.