A machinist ruler is an important piece of equipment for mechanics and others who need exacting measurements. Though the machinist ruler may appear to be very much like other rulers, the number of increments between inches or centimeters allow it to be read with a much higher degree of accuracy than standard rulers which don't feature as many increments. Reading a machinist ruler is easy, but may take a bit of getting used to for those who aren't familiar with how machinist rulers are laid out.
Place your machinist ruler into position next to whatever it is that you need to measure. If you are not able to place the machinist ruler directly next to the item that you will be measuring, place it as close as possible while making sure that it remains completely parallel to the item so that your reading will not be affected.
Check to make sure that the measuring system that you wish to use is closest to the item that you wish to measure. If you are using the Imperial or English scale (measured in inches) then you will want the side of the machinist with incremented inches closest to the item that you're measuring. If you're measuring in the metric scale (measured in centimeters) then you'll want to make sure that the incremented centimeters are facing the item.
Read the measurement on the machinist ruler. Depending on the ruler that you're using, the increments may be every 1/8", 1/16", 1/32", or even every 1/64" (or if using the metric edge, the ruler may be divided in 1 mm or 0.5 mm increments.)
Double-check your measurements to make sure that they were taken correctly; it may be best to pull the machinist ruler away and align it next to the item that you're measuring again, just to make sure that the two measurements match.
In addition to English and metric measurements, some machinist rulers are divided into decimal measurements. These rulers will still be marked in inches and centimeters, but the increments will be marked at 1/10, 1/50, or even 1/100 or 1/1000 of each inch or centimeter. When tightening springs or other connections, a machinist ruler can be used to precisely adjust the tension on the spring and make sure that the two pieces aren't too close together or too far apart. Simply keep the machinist ruler in place while making the adjustments in order to keep an eye on the movement of the adjusted parts.