1983 darmah

having checked my regulator with a multimeter with readings of 500 and 499 does this mean it is ok .my second question is my bike does not seem to have a motoplat voltmeter fitted will it be ok to run the bike without it.when I checked charge to the battery I was getting 13.5 rising to above 15 at 3000 revs I read somewhere that this means the regulator is duff any help would be very much appreciated .