You would need to enter +0.02 into the Z DRO if you wanted to make it go lower, remember you can only do that when the code is stopped.
The DROs can be used to add, divide, multipoly and subtract as well as just entering values, so for example you can do as above and add to the value already there or if you want to subtract you need to add a negative value, ie + - 0.02 would subtract it to multiply just use the * and to divide use /
Hood