The 7 white keys are named using the letters A,B,C,D,E,F,G. These then loop and repeat along the keyboard. It’s easiest to find a C first which is the white key to the left of any block of 2 black keys. From there, they go in alphabetical order to the right, up to G and then start over at A.

The seven white piano keys named A, B, C, D, E, F, G reflect the seven basic notes of the hydraulis. These notes were all the ancient Greeks needed because their tones create natural diatonic scales: a major scale when starting on C and a minor scale when starting on A—still the two most commonly used scales in western music.