Here is a suggestion...Post a pic! no just kidding. If you search google you will find printable paper rulers in the millimeter format. I would suggest printing and cutting a few. The paper is nice and pliable so you can get it close to the circles for a fairly accurate measurement. You will be off by a few mm...but it should be able to tell you what you have. If it is the 151 I would only keep them if this going on something that requires this period correct item to match the OEM bicycle. Otherwise use a set of 144 for easy parts sourcing.
Good luck.