Interpolating Masters

Can I create masters by interpolating between existing masters? I have an ultra black and a thin and I want to quickly create two masters inbetween them that I can then manipulate.

Thanks!

You can make instances and then select “add instance as master”

Page 109 of the handbook describes what you need to do in detail.

I tried this twice and it didn’t work, now for some reason after posting this it worked perfectly! Bizarre. Thanks!