Chainsaw Repair

Optivisor is the brand I use.    They have glass magnifiers and not plastic.   You can find them on eBay for around 36.00 dollars plus shipping.   There are different magnifications depending on what you want and working distance.
My wife has a pair she uses to thread a needle I believe they are DA 5 magnifiers.   I use a stronger one which are DA 8, but you have to be willing to work up close to your eyes with these.   

I did watch repair and restoration of pocket watches for 30 plus years and these visors are the industry standard.
I still have a collection of close to 100 pocket watches.  Two watch benches, 3 antique stake and sets, a watch lathe, jewel pushers, various tweezers and other tools.