It's not math, it is just add and subtract real simple. Measure the valve clearance to get the correction needed (plus or minus} and add or subtract that amount to the existing shim size to come up with the new shim size. When I did mine recently some of the existing shim size numbers were not readable so I had to measure them with a micrometer. I believe the discs are marked in MM. Don't sweat the guage stuff to much, you have a few thousands room for error. When I did mine I measured in inches and converted because that is what my feelers were.

It is quite possible you will find that none need adjustment.

After measuring and recording existing clearances I remove the cam to remove and install the shims as I find it easier.

Suggest you check condition of the "cushers" (the rubber things under the buckets. If they have hardened or fallen apart you should replace, engine will be quieter in the end.