Remember to measure from the top of the 12th fret to the bottom of the E strings. How you adjust your string heights will depend on the type of bridge fitted to your guitar.

I set the gauge around 1/2 inch ahead of the bridge and play each string to check if they're touching the bottom of the gauge. The low and high E should already be muted by the gauge touching them, ...

Put simply, it's the height your strings are set from the guitar's frets. If the strings are higher, they become harder to push down with your fingers – and that means the guitar is harder to play.