Calc Notes The error NaN means Not a Number. Basically an invalid result, re enter the values & recalculate.
The ID and OD of shims vary between the fork manufacturers. At times the shim sizes desired seem difficult to purchase. Manufacturers perfer to sell complete compression or rebound valves. Some suspension tuners will quite often be able to supply shims from their stocks but some do not.
Suppliers who are able to supply shims are Slavins Racing, Racing Suspension Products and Racetech.
WP Shim sizes and KTM Part Numbers. - WP Shim PDF
Beyond the basic calculation of the shim factor of an individual shim there is software available to assist in tuning suspension. One low cost product is Shim Restackor. This is on the bleeding edge so it is not for everyone.