Useful digital readout terminology everyone should know

Each specialty or area of the metalworking world has its own terminology—its lingo. Sometimes words can even mean something a little different depending on the context. For example, we know what “precision” means, but in the realm of digital readouts (DROs), “precision” may be defined as the closeness, or tolerance, of agreement among repeated measurements of the same characteristic, by the same method, under the same condition.

Let’s look at a few more terms from the DRO world that are good to know in the context of machine tools and readouts.

Reference mark

This is a pattern on the glass scale that is sensed by the reader head and is used for the Position-Trac™ feature or to quickly reset the readout system to zero.


Repeatability is the ability of the scale to return to an identified position within the specified tolerance. A repeatable scale is one that begins at zero on both an indicator and readout system; the table or tool is moved away from zero on both the indicator and readout system; when the table or tool is returned, both the indicator and readout system should again read zero. If this operation can be performed numerous times within a specified tolerance, the readout system and machine are judged to be repeatable.

Scale assembly

ACU-RITE scale assemblies consist of a glass scale enclosed in aluminum housing with sealed, die-cast metal end caps. To enhance glass scale durability, it is further protected from the environment by a recessed highly chemical-resistant, interlocking lip seal.

Reader head

Part of the DRO system’s encoder is a photo-electric device that converts the line pattern on the glass scale to a digital signal. The signal is the input the readout uses to display tool/workpiece position.

Zero reference

This is the point selected on or near the workpiece from which positioning is started, or in some cases, referenced for the entire machining operation. Zero reset is automatic or manual zeroing of the measurement (or count) displayed on the DRO. (Another term for reset.)


A sine or square wave signal whose phase differs by 90° with respect to a base signal, the quadrature signal is necessary for bi-directional counting.


This refers to the radius or diameter of a round cutting tool by which a dimension is modified in order not to over-cut or undercut the required dimension.


Metrology is the science and technology of precision measurements, often for the purposes of quality control. Tools like the ACU-RITE Edge Finder and touch probes are often used for in-machine inspection. 

Incremental measurement

Incremental measurement is between two successive points on a workpiece, usually, with a DRO system, incremental (point-to-point) positioning is done from a displayed preset dimension to zero, or from zero to the dimension, then the display is reset to zero. The SENC 50, SENC 150 and LMF 9310 encoders from ACU-RITE all use incremental measurement.  


Resolution is the smallest unit of motion that a readout system is capable of measuring and displaying. ACU-RITE readout systems are accurate up to 0.00002” or 0.5 microns.

You can continue learning about readouts, encoders and their efficient application by downloading The Ultimate Guide to DROs, or reaching out to our experts directly.