there is generally no math to be done that i know of. the syringes containing the medication are standardized and the doctors orders are usually on a pre-written form where the docs merely fill in the numbers. the pump computes the dosage for you. i would use the dose desired divided by dose on hand multiplied by the amount you have on hand (which is going to be the total amount of solution in the syringe) formula for any computations you would want to do. the first link below might give you more of an idea of how a pca is set up in it's pump. i found an example of a standing order as well. although this may not be exactly what you were looking for, i hope you find it helpful. your best information is going to come from being able to get your hands on one of these pumps and being able to play around with it. they are an odd animal--a bit different from iv pumps.