Coil testing

I had some problems with the ignitioncoil I used on the S90, it was an old CB72 coil but when it was replaced with a different type, my S90 ran better.
I really did want an original CB72 coil, as they were used n RSC90's back in the 60's and it looks good, so I had to test the coils that we have.
My SS50 was the answer:

I found out which of the 5 coils were good and now have an original CB72 coil on my S90 again.