How does the 6-month multiple entry visa work with regard to leaving and re-entering Thailand before the visa expiration date?

Hello!

I am currently on a TR 6 month multiple entry visa where each visit cannot exceed 60 days. So effectively I have to leave at least once every 60 days in that 6 month period.

Just before my first 60 days were up I went overseas and then returned to Thailand. My new visa stamp says it is valid until the 20 September.

My question is if I leave Thailand to visit a friend in Laos and come back before the 20 September date does it reset as my like second visit out of the country ahd therefore shortens my overall 6 months? Or will it be that the date I next have to leave by is still 20 September so whatever date I return from after that resets and starts my second 60 days.

I am really tired and hoping this makes sense!