Some useful links:
Dusty strings:
https://manufacturing.dustystrings.com/harps/accessories-hardware/tools-maintenance
https://manufacturing.dustystrings.com/blog/sharping-levers-camac-vs-loveland
Thormahlen Harps:
http://www.thorharp.com/pages/regulatingcamaclevers.htm
https://www.youtube.com/watch?v=kRcLPupXuIc
https://www.youtube.com/watch?v=sFKYjmmjzvM
Great set of articles about all sort of harp maintenance by Mike Lewis, here’s the link to the article on regulation:
http://www.harptech.com/Articles/Regulation/Regulation.html
Rees levers:
https://reesharps.com/regulating-rees-harp-levers/
Loveland levers (via musicmakers): https://www.harpkit.com/mm5/pdf/Instructions/Lever-1Regulation.pdf