Rosco Opti-Sculpt Calculator
I've recently (re)discovered Rosco's excellent Opti-Sculpt filters, there's plenty of good resources online about them and some wonderful reviews from others waxing lyrical about these magical pieces of plastic.
However, it surprises me that the official calculator for the resulting beam angle is an Excel sheet, which is a pain to use quickly on a mobile device, so I threw this together mainly for myself, might be useful for others.