The weight is there so maybe the spring is deformed but I'm not sure how much this helps if the head is too heavy in the first place and it's wound right back. I'll add a photo tomorrow if I get the chance.
Yeah, I've had the sapphire from Mike, I'm just less keen on importing blanks from further away as I'm UK based (though I guess it might not make that much difference between France and here in due course
![Sad :(](./images/smilies/icon_sad.gif)
I did end up buying a USB scope and was suprised how close the grooves seemed to be but haven't measured this properly yet. The feedscrew didn't seem crazy LPI so now I'm a bit confused, maybe still too much weight on the head. Maybe worth adding a dashpot? but really unsure of appropriate values.