Adafruit PCB Ruler
Handy reference for DIY printed circuit board design
The Adafruit PCB Ruler is more than just a way of measuring things. It is also the ultimate reference (at least for the size) for folks designing their own PCBs. The ruler is made of a 6” length of PCB laminate, and naturally it offers the requisite inches and centimeters. Where the ruler diverges from the expected is that it is covered, both sides, in reference materials for PCB design: want to know what a 24-mil trace looks like? What about a 28-gauge via? The ruler also has footprints for over a dozen surface-mount components like minuscule SOT-23 chips, the size of half a grain of rice. At $5 the ruler is a great deal anyway, made all the better by the fact that you can get one for free from Adafruit just by spending $100 in their store.
10/1/14Adafruit PCB Ruler $5