sherlock is right , i hope u have long stem on your compression gauge to rech the plug holes .
the engine should be hot and crank at 300 rpm .
u dont say what engine it is but here is a guide.
rb20e 1.23 mpa ( limit .93)rb25de 1.26 ( limit .96)rb25det1.2( limit .90)and rb 26dett 1.18 (limit .88) variance limit .10 mpa
crank the engine until the pressure does't go up anymore ( usualy a few seconds ) then record the reading it may be in psi on your gauge. 1 mpa =138 psi apr.
if u r pressure is down on 1 or more put some oil in the cil crank it a little then check pressure again if it goes up to normal it means u have worn piston rings , broken rings or chipped piston in that cil. if it doesn't make any diff then its leaking valve .
i hope that helps u in someway and as sherlock said dont wory if u r readings are low , maybe slow cranking speed or the gauge .
as long as they are all the same its good .
if they are all the same then put a little oil in the cil and try again if the reding is the same again its all good ( its unlikly that all valves are leaking the same amount .