Stamps on pint glasses

We’ve a small collection of pint glasses in our house (from three of us being bored uni’ students)

They all have a white stamp saying “pint” above a crown. This I take to be an official seal that its a proper pint in volume, is it? And the number below it changes depending on the type of pint glass, from tall and thin to the type you mostly get in the UK and Ireland. What is the significance of the number below?

A quick google for “pint glass stamp number” brought up this site.

Interesting stuff.

On further review of the site, there’s a link to a .pdf file with a complete list for you.

Extra info as to why these glases are used:

There’s legal obligations on landloards to ensure true quantities are served (pints, half pints, the stated size of wine glasses eg 175ml, 25ml spirits etc). By using stamped glasses, and ensuring they are filled properly, he removes any liability - ie if there is a manufacture flaw in the glasses and they aren’t a true measure, it’s not his fault. If he were using non-stamped glasses and this happened, it’s his fault.