How to use dial calipers ?

Dial calipers are like vernier calipers with a dial. This makes it easier to read for some people. The vernier scale can be small and you may have to resort to glasses or even a magnifier to read your vernier. The dial is pretty large and you probably won't have to squint to take a reading. While dials may be an advantage, it causes all sorts of problems. For one, all those gears and parts will eventually malfunction. Count on it.
For another, having a dial limits the calipers to being either metric or inch reading. That's no problem if you never need to switch systems. One or two models have attempted to combine both systems on one dial but that's confusing and bound to lead to errors.
Dial calipers offer four measuring capabilities: outside dimensions such as diameters measured with the large jaws, inside dimensions measured with the smaller jaws, depth measurements obtained with the extending rod, and step measurements taken with the front of the tool.
The ends of the jaws are beveled so that measurements in slots and grooves are possible. Don't use this area of the jaws for general measuring however, because it wears down quickly. Measure with the flat area of the jaws whenever possible.
The depth measurement is fine for small diameter holes and can extend all the way to 6 inches. If you need to span a larger diameter hole you can always get a depth bar attachment which will make your caliper function somewhat like a dial depth gage (see below).
Calipers have .001" graduations and are accurate to ± one graduation (per 6") if none of the measuring surfaces have been worn, bent or damaged. They're perfect for all sorts of quick measurement and can be used as a preliminary source before moving on to more sensitive tools such as micrometers (.0001"), depth gages or dial indicators (.0005" and .0001").
Calipers should be frequently checked for accuracy using a gage block, or gage block combinations. To check for wear in the jaws do this: clean them and close them. Then hold them up to the light and if they're worn you'll see light shining through the gaps. At this point, measure with the unworn surfaces or have the calipers repaired. These jaws can be ground flat again.
The most common dial calipers have a measuring range from zero to six inches. These are the most useful because they can be easily handled. However, 8-inch, 12-inch, and even longer calipers are available.
The inclusion of the dial makes for much easier reading because it eliminates the need to know how to read the vernier scale. The invention of the vernier scale is one of the unsung innovations of the past, but reading the scale requires some training and a lot of practice if you want to be proficient at it. It's best to ask someone to show you how to do this.
When taking a measurement, close the jaws o nly lightly, with pressure that is consistent from one reading to the next. You'll soon see that it's possible to fudge the results by just pressing a little harder. You don't want to do this. If you're new to calipers, it may be a good idea to practice on a gage block for a while to make sure you can get repeated measurements.
For quick reading, combine the numbers in A-B-C order, as shown above. (1.370" is the correct answer.)
The dial caliper is used to measure the inside or outside diameter of an object.Most dial calipers have a slide, slide lockscrew, thumb button, scale,dial with measured increments of 0.001 inch, and a bezel. For specific instructions on how to take measurements with a dial caliper, refer to either the manufacturer’s instructions or to tools and their uses. Regardless of what type of caliper you use, be sure to take the following precautions to avoid damaging the caliper:
1. Wash your hands before you handle the dial caliper to remove dirt and oils that might damage the caliper.
2. Wipe the caliper components clean both before and after you use the caliper.
3. Do NOT drop or otherwise mishandle the caliper. Doing so may damage or destroy the caliper.