just thread the gauge in finger tight.... most gauges have a rubber o-ring seal. either pull the kill switch or pull all the plugs out so the motor wont start. do one cylinder at a time and write down compression on each cylinder. turn the motor over several seconds. i normally get someone else to turn the key over and i watch the gauge. if will quit increasing pressure on the gauge when the cylinder max's out. i like to actually run the motor till it gets to operating temp before i do a compression check. that is the way i do it. i hope this helps