This 12” rule came highly recommended to me. After having used the 6” rule for a long time for just about everything ( it’s the one tool that’s always in my pocket ), I wanted the 12” rule. This was no easy feat as I don’t live in the US anymore and even on my recent visit back to the US, this ruler was difficult to find in your usual big box stores and actually I never was able to track it down.  I finally managed to get a hold of a few, ordered through Amazon for $6.98 USD( The General Tools website lists it at $8.75 USD).

These are touted as precision rules and it’s generally of fine quality, the markings are etched and in a nice contrasting black so it's easy to read and the markings are not likely to wear off.

It’s main advantage is that it is relatively thin and therefore very flexible. This makes it handy for getting into tight spots and in log building, for example, it’s great to be able to draw lines or measure round logs. For this, it is fantastic and I’ve found no other rule that is this flexible.

It’s got the usual graduations in 8ths, 16ths, 32nds and nicely 64ths for those who can see that small. Handily for me, it’s also got graduations in 1mm and 0.5mm. I tend to you use a mixture of both measurements.

What is most disturbing and disappointing about this ruler though, is that I’ve found the starting end of the ruler to have been ground or cut 0.5mm too short! ( see the picture ) Well, now that I know this, I guess I can work around it but it’s a rather inconvenient detail on a precision rule. I had bought two of these and I thought maybe it was just a production error on the one, but the other is identical. This definitely brings down the star rating for this tool as it doesn’t live up to its claim of being a precision rule.

As for flexibility and the usefulness in log building, that’s still a big plus. 0.5mm isn’t going to make the difference there but for fine woodworking, don’t rely on this rule if measuring from the end.

 What can you do if your measuring device is not accurate?

Although it would be nice if all rules were accurate and consistent out of the box, this not being the case what can you do? ( In fact even if they were - many rules being metallic - things like temperature can change them anyway ) Here are a few hints on how to work around differences in measuring rules or errors found like I did with this particular rule:

1. Don't rely on measuring from the end. Start your measurement from an interior mark, such as the 1inch or 1cm mark. Remember to add 1 (or whatever offset you used ) to all of your measurements. Learn to double check your measurements. Sometimes I'll re-measure using the (unreliable) end mark just as a rough check to make sure it's what I expected and to verify that I did the math correctly.
2. Use only one measuring device for all of your measurements. Use the same rule to measure the size piece that you need and the then again when setting up the table saw or when marking the board for a cut. It doesn't really matter what the actual number is but rather than the fit is correct. 
3. If you're using more than one measuring device, check them against each other and make sure they all read the same. In most cases it doesn't really matter whether your measuring devices are spot on with the reference standard, but rather that your measurements are consistent. This way, it doesn't matter which device you pick and use, you'll get consistent results.
4. Avoid the use of rules if you can. How can you do this? Use a measuring stick Transfer your measurements onto a scrap piece of straight and flat wood or metal extrusion or bar. Use this same device for setting up the cut. This has the advantage of avoiding numbers altogether, reducing the possibility of introducing error by forgetting the number or reading it incorrectly.  This is a handy hint in any case when it's difficult to get a rule in the space you are measuring (either because your rule is not long enough or there is not enough physical space ) - for example measuring the inside of a drawer or cabinet.