Scale 1:25 or 1:75 why scale ruler first reading is 0.5m and 1m respectively ?

Dear folks

Yes I do understand scale ration 1:25 means 1 unit on a map equal to 25 units on a real and scale ration 1:75 means 1 unit on a map equal to 75 units on real

Question my Kent tri scale ruler showing first number for ratio 1:25 as 0.5 m (i.e 50 cm, 500 mm) while first reading for ratio 1:75 as 1 m (100 cm, 1000mm) ?

My confusion for the ratio 1:25 ruler has 25 small tiny line between 0 and next reading means 25 units right ?? if I multiply 25*25 = 625 why scale reads it as 500 mm or 0.5 m????

Same thing for the ratio 1:75 ruler has 20 small tiny lines between 0 and next reading means 20 units right ?? if I multiply 20*75 = 1500 why do I have 1000 mm or 1 m ????

Thanks
Thanks