The Meazure program provides a number of measurement units. However, it may be desirable to perform measurements using a set of units that Meazure does not provide. For example, when measuring distances on an online map, it may be useful to use the map's scale to provide measurements in miles. This can be accomplished using Meazure's custom units capability.

A custom unit of measure consists of a name for the units and a scale factor. The Meazure program stores these parameters so that the custom units are remembered between runs of the program.

To access the custom units preferences panel, select the Define Custom item from the Units menu. THe panel can also be accessed by selecting the Preferences item on the Edit menu then select the Custom Units tab on the Preferences dialog.

The first step in creating custom units is naming the units. Enter the full name for the units in the top text field. This name is used on the Units menu to identify the units. The name can be up to 16 characters. In the Abbreviation text field, enter a two letter abbreviation for the units (e.g. mi for miles). The abbreviation is used to identify the units on the Tool Information and Screen Information sections.

Once a name and abbreviation for the custom units have been entered, the scale factor section of the panel will be enabled. The scale factor is used to convert the custom units to and from a set of units already known to Meazure. The scale factor can be applied directly to pixel measurements or can be applied to a resolution independent set of units such as inches. The scale factor is applied in the following manner depending on the text field selected.

• Pixel-based:
  length_custom = length_px / scale factor_{px per custom}
• Inch-based:
  length_custom = length_px / resolution_{px per in} / scale factor_{in per custom}
• Centimeter-based:
  length_custom = length_px / resolution_{px per in} * 2.54_{cm per in} / scale factor_{cm per custom}

Note that accurate measurement using custom units based on inches or centimeters depends on the accuracy of the screen resolution used in the conversion. To ensure accurate measurements, calibrate the screen resolution for your system.

It is likely that you will need to specify the number of decimal places to display for custom units measurements. To set the precision of these measurements, press the Set Display Precision button. This will display the Precision preference panel allowing you to specify the number of decimal places to display for each type of custom units measurement.

Once custom units have been defined, they can be used by selecting name of the units on the Units menu. The name on the Units menu corresponds to the name entered on the Custom Units panel. Once the custom units are selected, the abbreviation for the units is displayed beside each measurement text field on the Tool Information and Screen Information sections.

If custom units have been defined and are no longer needed, they can be deleted by pressing the Clear Units button on the Custom Units preference panel.

For example, an online map uses a scale of 0.5 inch equals 1 mile and we want to perform measurements in miles. Select the Define Custom item on the Units menu. The Custom Units preference panel is displayed. Enter "Miles" for the name of the units and enter "mi" for the abbreviation. The scale factor portion of the panel is now enabled. Since the scale factor is based on inches, select the middle radio button. Enter the scale factor 0.5 since half an inch is equal to one mile. Press the display precision button and adjust the number of decimal places to display as needed. Press OK to close the preferences dialog. Finally, select the Miles item that now appears in the Units menu to perform measurements in miles.