What is 1/4 step down tuning?
If you have an electric tuner, simply drop the pitch of each note down by around 40Hz to achieve quarter-step down tuning.
What Hz is 1/4 step down?
1:4 tone below 440 Hz is 427.5 Hz.
What is a quarter step down from 440?
Do you know for sure it's exactly a quarter step? A = 440 Hz, G# = 415.3 Hz. Halfway between those 2 numbers is 427.65 Hz.