Chevrolet: Power assisted brakes, minikie, power brakes

Question
Sitting at a red light my pedal slowly goes down an inch or so.        When I do the 3 tests to ck the power brakes all seem OK, except while holding brakes on after stopping engine, then starting up again the pedal drops an inch>. The books say "should drop a little" how much is a little ?   1997 Prizm but probably same as most Chevys

Answer
OK
I WISH I CAN SAY DO NOT WORRY ABOUT IT , AS MY 99 CHEVY PICK UP DOES THE SAME THING AND MINE GOES EVEN LOWER THAN YOURS AND TWO WEEKS AFTER I GOT IT FROM THE DEALER I HAD A 11,000,00 WORTH OF DAMAGE DUE TO THAT DAM PEDAL BUT I NOW STAY A BIT MORE AWAY FROM THE CARS AND STOP A BIT EARLY AS THAT IS HOW THOSE DAM BREAKS WORK BUT I WOULD REALLY BE ON THE SAFE SIDE AND GO TO A PLACE LIKE MIDUS OR MINIKIE AND TELL THEM TO JUST LOOK AT YOUR BRAKES AS IT WILL COST YOU NOTHING FOR THEM TO LOOK THAN I WOULD FEEL BETTER.AS I SAY MINE DOES IT ALSO AND IN THE RAIN ON WET ROADS IT IS EVEN WORSE, BETTER BE SAFE THAN SORRY