You haven't given much information so I am guessing what your problem is:

The DIV function in LAD is:

The Divide Instruction (DIV) divides a 32-bit signed word integer stored in A and A+1 by a 16-bit signed integer in B. The quotient is stored in R and the remainder is stored in R+1.

This is propably not the result that you want. In the Special Function Programs you can create an equation to divide one speed by another to get a ratio. It might look something like:
V100. := WX101/WX201
Remember the period after an address signifies it is a real variable.!

I have attached a few pages from the 545/555/575 Programming Reference manual on the SF math.

Good Luck,
billwest