hello,
I was given a few small transparent magnifying glasses by a student friend "stone kicker". I was informed that the "stone kickers" use these in the field for viewing up close stones/agates etc.. they find. A brief description of the magnifiers, these are plastic transparent plexiglass ( acrylic ) actual size : 59mm x 29mm x 7mm effective diameter: 25mm weight: 4g magnification between x5-10 times. I was very fortunate recently to have the opportunity in between heavy rain showers to practice fire lighting skills in the woods whilst out walking. It's such weird weather in between showers it was brilliant sunshine +17C. I decided I would try this small magnifying glass with char cloth & amadou as tinder. They are used primarily by students in the laboratories at University & are thrown away after use. These are very similar to those found as GAWs in cereal packets etc.. I was given a few samples brand new in zip lock plastic bags for Bushcraft purposes & for such a small lens BTW they are very effective. I would say IMO they're very similar to the magnifier from the Swiss Army Knife.
Regards
David