I just got a new tape measure and notice something I have never noticed before. There is a small diamond shape marking every 16 inches.
What is it marking? Is this some lost (or rarely used) unit of measurement, like a cubit or something?
Standard stud and joist spacing in modern construction (for at least the last several decades) is 16" on-center.
Former framer checking in.
Actually most tapes have 16" OC (on center) marks designated in red. 16" OC lets outside shear material and inside shitrock panels fall easily on stud centers, since those materials are generally in 8 or 12 foot lengths.
The small diamond marks, on the other hand, designate 19.2" OC, if your tape is anything like the ones I’ve seen. This gives five studs per 8 foot run. I’ve heard it’s some federally used standard, but that is just job site scuttlebutt. Personally, I’ve never built a thing with those centers, let alone seen a drawing for same.
Go figure…
New tape measures still have inches?
In the US they do, since that’s the de facto standard for the construction industry. Some also come with a metric scale, as well, but carpenters rarely use it.
As MonkeyMensch suggests, most tapes have 16" centres marked in red, and little diamonds on the 19 and whatever (something like 13/64) inch spacings, but I’ve seen tapes with 16" centres marked with long skinny diamonds and the 19" ones marked with short fat diamonds. I’ve never seen anything built with the 5 studs per 8’ either - always either 16" or 2’ centres.
I’m from Canada and all for metric to boot, but I find metric scales on tapes very annoying (assuming I’m using it for construction) since you can’t read off both edges of the tape, plus you don’t usually get both feet and inches plus total inches, and I hate converting between those in my head. Too bad we can’t frame on 40cm or 60cm centres using 1.2m x 2.4m sheeting. 
But till that day, I don’t wanna see any metric on my tape measure.
Oh, that’s good, Gorsnak. 
This Straight Dope Staff Report may be of interest: On tape measures, why is there a special symbol every 19-3/ 16 inches? (24-Sep-1999)
Here’s an example of a span table (pdf format.) Values are given for 12", 16" and 24" spacing, as is typical.
I’m pretty sure that 16" spacing predated sheet goods; it was already the standard when my father learned carpentry in the Thirties and Forties. My guess is that laying studs and rafters out on 2’ centers let the roof and siding sag and nobody wanted to cut all those boards for a one foot spacing. 16 inches was a nice number in between the two.
I was kinda hoping this was going to be about Karen’s belt size.
I think it’s been covered for the most part, but 16" is simply a factor of 4’. Which is generally used in construction. Sheet goods plywood, etc. usually come in 4’x8’ sizes. Most framing lumber will be in lengths (8’ and 12’ etc.) that are evenly divided by 4’ or 16"
As Cornflakes said, rafters and joists spaced at 2’ intervals are generally weak when using standard lumber. Although I have built a lot of structures with rafters spaced at 2’ and even 4’ any more than that starts to really get expensive though.
a cubit…heh that’s pretty good
Strange markings…Did you find it near Roswell, NM by chance?
I think I am right in saying that here in the UK, although officially metric, we still have all our building materials in the old metric sizes but converted to stupid multiples of metric units. Too expensive to change it all over I guess with such an existing housing stock requiring maintenance…
Give us an example
It’s good for the soul to admit it when you are wrong. I have tried to find some support and failed so it looks like I was talking bull. My only excuse is that my father was responsible for telling me and as an architect you would have thought he would know. But as he retired in 1988 I guess we have finally fallen into metric line even in the building industry (if you will give me the figleaf that what he said was true at least when he was working).
Anyway, I withdraw. Continue all… 
I can be more specific. The diamonds are definately at every 16 inches, not 19.whatever.
I am in Canada, but the measure doesn’t specify if it was made here. IT does, however, have both metric and imperial. IIRC, it has centimeters, meters, and fo rsome reason millimeters but only up until the first 30 cm or so, plus it has feet, inches, and a runinng total of inches (so it says both " 1’ 3" " & " 15" ".
Anyway, if it is to mark stud centres, I guess that’s only useful if building a wall? Otherwise, I can’t think of any practical reason why A) I’d care where the next stud is and B) It would be so hard to remember “16” if I did need to know.
Karen’s waist size?
Marking stud and rafter centers is what framers do all day, and they’re the ones who give tape measures a workout. It’s easy to remember to mark every even foot for 2’ centers and every foot is marked, but there would be a lot of errors if every framer had to remember their 16s multiplication table for every wall (actually, they would probably mark the tape, at least I would.)
Yes, do UK (and other countries’) carpenters still work mostly in feet and inches? Is the standard sheet there 4’x8’, or some hard metric conversion that annoyingly doesn’t match old work? I can see more problems with a conversion than it would solve.