In the old days, hams with FT-243 or similar type crystals would make small frequency adjustments by grinding one of the crystal faces to increase the frequency. Sometimes they took the process a little too far. What was a common method used bring the frequency back down a bit?

rub pencil on the crystal

tighten up the crystal case or spring

grind the edge of the crystal

put the crystal in the holder upside down

Answer: Rub pencil on the crystal. Been there, done that too!