Durometers - Am I loosing the plot??


What is the conversion between Shore A and Shore C?

I am measuring a piece of foam which i know is 25 Shore C with an A gauge and it is saying 15 shore A which works as A-C should be +10? then I measure it wiht a shore C gauge and it comes out as about 3C. All the charts say 15A is about 3C. Im really confused. Are there different scales of C?


Sorted it now. oops.