Path length for curves, perimeter of polygon

[sillyScientist]

I use affinity to make some scientific figures and do some basic data analysis, and it would be really nice if I could draw a curve or polygon on data and then measure the total length of the curve. As it is, I implemented it myself in bokeh, but it made me sad. 

[ra.skill]

+1 for a way to measure/know the length of a curved path or stroke. I use Designer for technical patterns to scale and need to know exact lengths sometimes.