Tuning my Guitar to my Record Player

I been tryin' to tune my guitar to my stereo. The record player plays slow; it's an A flat when it should be an A, but not quite, so it's hard to tell just where the tuning lies; I'm tryin' to get it perfect. I used to have a keyboard in Savannah that would really come in handy here; it would adjust by cents. I could get the keyboard perfectly in tune, and then tune the guitar to it. The guitar is a much more temperamental instrument; it's much harder to tell when you actually have a perfect tuning.