discount calculation rules for different subtotal prices

[Pascal1978]

I had different discount rules for subtotal prices.
for example: 5% discount if subtotal is above 200; 10% discount if subtotal is above 500 and 15% discount if subtotal is above 1000

in VM 2.0.20c i had math operation D-5% or D-10% etc...
now VM 2.0.24c gives an error so i have to changes the rules, but i can't find out what is has to be to work properly