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 TIMING Light Model # 7 Bakelite USA Parts Repair As Is
Vintage Harvey E. Hanson Compression Tester Model 5 w/ Original Box (1963)
Vintage Harvey E. Hanson Co. Model 5 Compression Tester In Box Made In USA
Vintage Harvey E. Hanson Compression Tester 16455-1 Model 1
Vintage Harvey E. Hanson Co. TL-324 Power Timing Light Chrome Paw Paw Michigan
