I wonder if you could use a laser tachometer to help dial in the RPM? e.g. https://www.amazon.com/Digital-Photo-Laser-Tachometer-Contact/dp/B001N4QY66 https:/

I wonder if you could use a laser tachometer to help dial in the RPM? e.g. https://www.amazon.com/Digital-Photo-Laser-Tachometer-Contact/dp/B001N4QY66 https://www.amazon.com/Digital-Photo-Laser-Tachometer-Contac...