This is just a simple sample explanation of how to take measurements of physical objects in the Manufacturing (Tools Skills) Lab including mechanical parts with the use of a marking pencil, metal scriber, and ultimately a (Sharpie) ”magic” marker: Before anything I would make sure I have a clear safe place on the desk or bench where I will lay the materials, parts, and instruments I will work with. Be certain you have enough flat space to place things horizontally on with great care. Now the following general guidelines as suggestions:
(1) First rule of thumb I recommend is to know what are the two exact lines/marking points between which you are measuring.  You can estimate/take a reasonable estimate without even yet having a measuring instrument in your hand. But your official measurement will involve having either a ruler or combination square(contains a handle with a 45-degree angle)
(2) It is a good idea to know before-hand what units of measurement are to be used. For example in our class, we will be using the English system of units to measure lengths in inches. Therefore the ruler or combination square you use should have markings/intervals set for “inches”. If you use the metric scale of a ruler (often in either centimeters and/or millimeters), then your measurement will not be in units of inches, which means you will have to take extra steps to perform a mathematical calculation to convert from one unit to the other. For instance: you may have to use the following conversion factor: 1 cm = 2.54 inches. So if you measure something that is 2 centimeters long, then you will have to calculate that it’s equivalent to about 5.08 inches. But if a measurement requires exactly 5 inches, then using the 2 cm indication from the ruler will not give the most accurate or precise measurement, which may lead to overestimating or underestimating a length. At some point this can result in finding something to be either too short or too long. Or when cutting a piece of metal, a slight error can cost you some serious rework due to ending up with something that is either too short or too long.
(3) Once you know where the two lines/points you are going to measure between, you will likely proceed to look at your measuring instrument’s “zero” (0) reference line and line it up as close as possible to the first(and best) reference point you choose. Then align the ruler/combination square while holding end closest to the point as tightly as comfortable without seriously altering the relation that you first set up between the reference point/mark and the zero(0) of the ruler/combination square. If anything seems to slide out of place, just carefully try sliding and/or rotating it as best as possible. Note: Although you can only be so accurate with the measurements you take, it is important to have enough appropriate lighting in the room to help you see small points/markings in relation to the measuring instrument. Also try not to let shadows of edges block your field of view as they may easily distort your perception of how “long” or how “short” something actually is.
(4) Once you have looked at the reading on the ruler that indicates exactly how far one point is from the other(which is next to “zero” marking of a ruler), you may want to mark it lightly with a marking pencil (or metal scriber if your are working with a piece of sheet metal). You may want to double- and even triple-check the length you observed and write it down on a suitable place of your notebook, lab manual, or other piece of paper. Upon doing this you may also write a log of what exactly you have been measuring and get a second opinion (from appropriate persons) before taking any drastic action like cutting, punching holes, bending, or even scribing too deeply.
Happy measuring!!!
