I've been producing some calculations for frequency and rpm of accessory pulleys on an engine. I started off using the engine idle speed (rpm) 750 - 800 and mathematically calculated a desired Hz range of figures of 12.5 - 13.30. The actual engine frequency is 13.20 Hz. I moved on and calculated the water pump frequency between 16.35 to 17.43 Hz and the actual frequency is 17.30. I also worked out similar calculations for the AC system rpm etc. My problem is, when I did this at the beginning of August this year, I now can't remember how I did it! Any help appreciated to jog my memory, and I promise I will start to write things down so that I can recall them to memory when required. Thank you.