List of Optical Formulas: Link

https://www.opticiansfriend.com/articles/equations.html

Online Video Series by John Seegers (Subscribe to this): Link

https://www.youtube.com/channel/UCdfKXBLjBDbX2X2g0XuAbmw

Optician Works Study Guide from Laramy - K (PDF) : Link

 https://opticianworks.com/wp-content/uploads/2016/10/ABOGuide7.22.2016R.pdf