Double post from another blog topic, but wanted to put it somewhere I could readily add to later. Here goes!
A very incomplete review of folding rules, and there are a number of variations. The first picture shows a vintage stainless steel Lufkin Rule Co. No. 1174 EM. It's an outside measure rule for English, and inside measure for metrics. Don't know how old it is.
Another rule in the picture is the Lufkin Two Way, Model 966. It's an inside rule through and through, and reads from left to right and right to left as you may need it. Never read numbers upside down again! Really cool, and really hard to find.
The next pic shows the problem of the 066F model Lufkin; it's an inside rule too, but reads upside down if you're measuring from the right end of a project.
Last up is a real outside measure ruler. The Stanley #426. Aluminum, cool looking, but very impractical.
Finally, a trick that my grandad used that I continue to use: filing a small notch in the brass ends of stick rulers provides for a very handy nitche for the pencil tip to ride in when striking a line (like using a panel gauge).
That's all I wanted to add to this topic. Thanks for looking!