I just got a new resonator guitar which had a nice set of strings. The set-up tag that came with it indicated it could take either light or medium strings.

When it came time to change strings I couldn't decide which to put on, and I had no way to guage what was already there. (I ended up putting on light, and they don't have quite the same sound>)

Other than an extremely expensive micrometer, does anyone make a cheap but accurate string guage for determining unknown sized strings ?