[TheForge] Forge Geometry- calculating a radius

[Fiorini & Skiles]

I was trying to figure out how to accurately measure an existing radius for 
a curved railing. I came across this formula from 
http://www.johncglennon.com/papers.cfm?PaperID=17

R = Lsquared /8m + m/2

Where

R = the roadway curve radius, feet

L = the chord length, feet

m = the measured middle offset, feet

This particular website was actually demonstrating another method that was 
more appropriate for road work. But the formula above seemed like it would 
be fine for the curve I'm dealing with.

Does this work accurately for a railing curve, when you've got the curve all 
laid out, easy enough to measure? It gave a close, but about 3 inch 
different number than our rather inaccurate 
2-people-pretending-to-be-a-compass method. I'm planning to go by the 
mathematically calculated number.

Is there a better way? Will that geometry give me an accurate result? Are 
there any other good websites or books on construction geometry?
Thanks,
-Kirsten
www.knitsteel.etsy.com