7g+9.7g=16.7g does not work in case of effective mass calculation:
1)the mass of shell is not centred on stylus point
2)weight is reduced to 80-90% as seen from stylus point.http://www.fl-electronic.de/analog/tonarme.html
based on HiFi Choice indicated 14.5g
The correct calculation shoule be:
weight * SQRT(location of shell from pivot^2/effective arm length^2)
This can be applied on the mass of cartridge: actual effective mass of cartridge as seen at stylus point is reduced to around 90%.
The above equation is not usable at user end. Effective mass of arm is often misunderstood in such a way.
In any case 14.5g or 16.7g as arm mass is no problem for low compliance cartridges.