tone arm with 10gr mass with 15 gram weight cartridge?

um = micron = one millionth of a meter.

if that was the question.

You can practice on the calculation chart that @yugiboy has posted.

With a well tempered you have variable damping to play with too, the raw resonance calculated for an undamped arm using the common formula won’t be the whole story.

http:// korfaudio.com/blog70

ok thanks everyone, i'll try to do my homework.
  

@stone1 , If you stick with arms on the lighter side, effective mass around 14 you can always add mass to tune the system. There are test records like the HI FI News Analog Test Record that have vertical and lateral resonance tracks that will give you a very good idea where you are. Then you add head shell weights until you get the lateral resonance down to 8 Hz or so. I like below 10 Hz as in my experience the bass is better. The published specs can only give you a ballpark idea of where you will be. There is enough variability to make accurate measurement of the pairing a much better approach.