Question For The Pros

Seamus! Cork!

Your help, if you please!

On the Guinness pint glass we have found a small circle with a wavy line through it, with numbers top and bottom... any idea what they stand for? Our bartender last night couldn't help us- thought it was maybe a mixture formula... We plan to ask when we tour the Guinness brewery, but thought we'd check with the experts! :o)

Molly O'Shea