Is it two turns, then one, then two? Is the last one not a full turn first? I always forgot and it always took so many tries to get it right.

For an old one maybe. Mechanical is usually accurate to way more precise measurements than that. Even back then it would be measured in a few seconds. Not a minute.

Getting this was serviced by someone who knows what they re doing may make it way more accurate.

Do you have a photo for when it's fully cooked?

That one needs quite a bit longer to fully obsorb the liquid! (though I'd be a bit concerned since the mussels look fully cooked but there clearly needs to be more cooking time.)