Broken rings usually won't drop the compression all the way to zero. That takes a badly burned or stuck valve, or maybe a hole in a piston. Air pressure at the spark plug hole with the piston near top dead center on the compression stroke will pinpoint the source of the leak. Put the transmission in gear and set the parking brake, or clamp the flywheel to keep the air from turning the crankshaft.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!