Arrive at the pitch from BELOW. If you overshoot, drop well under and come back up.
A tuning machine, the nut slot and the string wrapped round the post all have slack in them. Coming up to pitch pulls that slack out and leaves the string under tension against the post, where it stays. Coming down to pitch leaves the slack in, and the first bend or two of playing takes it out for you — which the string pays for by going flat.
It does not rescue a string that is genuinely worn out, and it will not survive a badly cut nut slot that binds: there the string sticks in the slot and releases in jumps whichever way you approach from, which is what a pinging noise while tuning means. A new string keeps stretching for hours whatever you do.
Estimate with the rule, then check it against the calculator that models it properly.
Open Guitar Tuner →Arrive at the pitch from BELOW. If you overshoot, drop well under and come back up. A tuning machine, the nut slot and the string wrapped round the post all have slack in them.