There are endless variations in the dials used on mechanical dial indicators. In most cases, though, they can be broken down into two distinct styles: balanced and continuous. Let’s look at both.

With a balanced dial, the graduations around the dial represent the smallest value, or resolution, as marked on the dial face. The numbers on the indicator face are an aid in counting the value of the divisions, usually grouped by 10, but also representing 2, 5, or 20 steps around the dial.

In reading a balanced dial indicator, keep in mind that you are using a comparative indicating device, and the indicator reading usually means nothing by itself. The indicator reading must be added to or subtracted from the value of the reference or master to which the gauge was set.

Mahr Millimess 1022, balanced dial

Revolution counters are those extra little hands-on indicators that keep track of the number of times the big hand completes a revolution. These may seem a little strange, because the typical ANSI balanced dial indicator has less than three revolutions available, but it’s much easier than it might seem to miss a revolution. A warning that the indicator has gone through, or not reached its “zero” point, is helpful in preventing bad parts from being accepted.

However, the warning can also tell you more than that. The revolution counter can tell you whether the indicator is within its measuring range or in the pre-travel or over-travel area. It can warn you that the indicator might be too high in amplification for the application, and that perhaps a slightly longer-range, lower-resolution indicator would be better. Or it can provide an indication that something has shifted in the gauge setup, or even that the part being measured is out of control, indicating that something in the process has shifted.

On the cautionary side, the revolution counter shouldn’t be relied on too heavily as a measurement device. The counter is small, so using it as part of the measurement is not always reliable. And, as with all mechanical indicator specifications, the longer the range, the more open the performance tolerances become. On balanced dials, use revolution counters for their intended purpose: a warning indicator. They can be a sure sign that something is wrong.

Continuous dials are usually found on long-range indicators that typically have more than the standard 2 1/2 dial revolutions. Some may even have extremely long measuring ranges. The dial is read much like a balanced dial, but there are no minus readings and, generally, there are larger numbers. Long-range dial indicators will almost always have a revolution counter. Here the revolution counter is invaluable. It’s used to keep track of the number of times the indicator hand has moved past zero and does it much better than your eye could. With a combination of the revolution count and the graduation count, a measurement can be determined.

Mahr MarCator, continuous dial

The range of these indicators is a valuable characteristic in many applications. Typically, long-range indicators will be used on a bench stand, allowing the user to measure a wide range of parts using the base as the reference point. The long-range indicator can also be used on a machine to monitor the position of a slide to aid in manufacturing a part. Both are acceptable applications.

Keep in mind that long-range dial indicators are also comparative instruments, even though they may have measurement characteristics. Used improperly, they can cause potentially serious errors. As noted, the longer the range is with these indicators, the larger the acceptable error. In some cases, a 2% error is typical. Because 2% of 4 inches is 0.080 in., this level of inaccuracy could constitute an error larger than the tolerance range on many parts. The proper way to use the indicator would be to set the gauge with a master at 4 in. The rev counter and the hand might be set to zero as the 2-rev position for its starting position. Then the gauge would act as it was intended—as a dial comparator.

Published July 2, 2025, by Mahr.