G. C. BHARUKA, J. ( 1 ) PETITIONERS are owners of omni buses. As such they are liable to pay tax under Section 3 of the Karnataka Motor Vehicles Taxation Act, 1957 ('the act' for short) read with item No. 8 of part 'a' of the schedule to the act. By Karnataka Act 14 of 1989, the measure for determination of tax liability in cases of omni buses was changed from seating capacity to the floor area. Constitutional validity of the said amendment was upheld by a division bench of this court in the case of Sree Gajanan Motor Transport Company Limited v State of Karnataka and others. The said judgment was subsequently affirmed by the Supreme Court in civil appeal No. 4728 to 4775 of 1990 disposed of on 22-11-1991. Accordingly, the authorities under the act measured the floor area of the vehicles in question and raised the impugned demands. ( 2 ) PETITIONERS have challenged the said determination and assessment of tax by asserting that the tax can be levied with reference to only such portion of the floor area of the vehicle which can be said to be available for erecting seats. According to them, this can be only within the wheelbase as specified by the manufacturers. ( 3 ) ON the other hand, Mr. H. g. ramesh, learned additional government Advocate has submitted that the floor area in its common parlance could only mean the overall length multiplied by overall width of the vehicle and that can be the only basis for ascertainment of tax liability under the relevant item of the schedule to the act. According to him, it is wholly immaterial whether the floor available within the body of the vehicle can be used for sitting purposes of passengers or for installing the machines or the seat of the driver or has been depressed or raised for any other purposes. He also invites my attention to the definition of the floor area inserted as explanation (6) to the schedule by Karnataka Act 10 of 1991 with effect from 1-4-1991 to impress his said point of view. ( 4 ) ACCORDING to the dictionary meaning 'floor' means lower surface of a room or platform of a bridge, etc. Accordingly in the context of the vehicles, it would mean the lower inner surface of the vehicle irrespective of the use to which surface is put to. ( 4 ) ACCORDING to the dictionary meaning 'floor' means lower surface of a room or platform of a bridge, etc. Accordingly in the context of the vehicles, it would mean the lower inner surface of the vehicle irrespective of the use to which surface is put to. Whereas, the wheelbase as demonstrated by the petitioners themselves means the distance between the two axles of a vehicle. Therefore, in all these cases floor area of the vehicle has to be necessarily more than that within the wheelbase, and such area has to be comprised of wheelbase area plus the areas covered by the rear and front overhangs, ( 5 ) RULE 93 of the central Motor Vehicles Rules, 1989 which provides for dimensions of the motor vehicles makes this aspect quite clear. ( 6 ) IN the above view of the matter, floor area, in the absence of any statutory definition to the contrary, has to be taken as the total area of the floor inside the body of the vehicle. At the material time, the legislature in its wisdom had provided such floor area to be the basis or measure for computing the tax under the act. Various vehicle owners were assessed and taxed on that basis. When challenged, the said provision and the assessments made thereon were constitutionally upheld by this court and ultimately by the Supreme Court as noticed above. ( 7 ) IN the said view of the matter, I am of the considere dopinion that it is not permissible for the petitioner to now contend that a different meaning should be assigned to the said expression 'floor area'. ( 8 ) BY the Karnataka motor vehicles taxation (Amendment) Act, 1991 (act 10 of 1991) which came into force with effect from 1-4-1991, 'floor area' was defined by inserting explanation (6) under the schedule to the Act, which reads as under:" (6) the expression 'floor area' means, the total floor area inside the body of the vehicle (measuring length into breadth) less ten per cent standard deduction of the total floor area: provided that fraction of a square metre beyond the first decimal point of the net floor area arrived at after standard deduction shall be rounded off to the next higher decimal point. Example: (1) 1. 31 to be rounded off to 1. 4 (2) 1. 76 to be rounded off to 1. Example: (1) 1. 31 to be rounded off to 1. 4 (2) 1. 76 to be rounded off to 1. 8 (3) 1. 654 to be rounded off to 1. 7". ( 9 ) SO far as the aforesaid definition of 'floor area' as provided by act 10 of 1991 is concerned, in the absence of any specific provision making it retrospective, it is necessary to be held as prospective in nature through the said expression 'floor area' has been added as an explanation to the schedule. It has to be so held because it touches upon the measure or unit of charge and that forms an integral part of the charging Section itself. In effect, by giving an artificial definition to the expression 'floor area', the legislature had intended to grant a standard deduction of 10 per cent of the total floor area thereby reducing the tax liability to that extent. ( 10 ) FOR the said reasons, in my opinion, the contention raised by the petitioner in these writ petitions are devoid of any merit. Writ petitions are accordingly dismissed. --- *** --- .