From picture on the Left, place solder through spark plug hole, keep solder leg going Left to Right or Right to Left for orientation puposes. It is important to keep the solder leg over the Wrist pin, and not from the exhaust to intake. Keeping it over the Wristpin prevents the piston from rocking and giving you a false reading.
Picture #2 shows solder in the Dome area all the way to the outside of the Dome. Picture #3 shows solder up against cylinder outside bore, on the wall and resting on the Dome. Hold solder in this position and work piston up through its stroke to squash solder.
Remove solder and measure at its tip, the farthest point that contacted the cylinder wall. Use a Micrometer or Calipers to measure squashed thickness. Picture #6 shows how the 'squshed' solder tip looks.
The measured thickness is your squish clearance using the SQT method. Picture #4 shows a .039" thick squashed solder tip.