The other issue is that it leak off pressure fairly quickly once disconnected from the open spark plug hole. If you can read it while doing the test all is well, but it will not hold it for you for a future reading.
Vintage Harvey Hanson Model #5 Compression Tester 0-300 PSI
Vintage Harvey Hanson Dwell Angle Gauge 113-11
VINTAGE HARVEY HANSON TIMING Light Model # 7 Bakelite USA Parts Repair As Is
Vintage Harvey Hanson Vacuum & Fuel Pump Tester #2 Original Box +Manual
Vintage Harvey Hanson Model No 15 Starter Current Indicator Amp Gauge
