There are some custom versions of the T24-HS that have a dual unit function enabled. Most of these will have different keypads showing the Units button.
The top left button activates this feature. There are two annunciators used for this so usually get added to the custom label with lines showing which enunciator is which unit (Customer would put unit in clear window)
The default state is the normal value as transmitted from the linked device. Clicking the button toggles between the two units and the second one actually uses the custom display scaling of the handheld device to calculate the second of the units. This is configured in the advanced section of the toolkit. (Note that overload settings in the handheld are all in the original units)