I want to get segment size, but I cannot get it.

When segment size is null, it is automatically set.
but I just want to get specific segment size.

Looking at the function 'updateSegmentSizes' in code, segment sizes are set to startAngle and endAngle.
I found out endAngle minus startAngle is segment size. then, I want to set the specific segment size in addition to the current size.

but I don't know what to do next. 
Please help me!