I have a client that likes the "arc" gauge widget. I can't figure out the decimal formatting on that one. Some tags display a decimal, while others show a whole number.

Some of the gauges let you specify the number of digits to display after the decimal. How can I set that on the arc gauge? Is there an expression to use?

I may be mistaken but I believe this widget only shows decimals for numbers less than one. If you want to see a decimal, you deselect show value and add a new number, with your own formatting, using the numeric value widget (Text -> Numeric Value). Once you get this looking like you want, note that you can always save the combination of these widgets as a new widget by selecting the components, right-clicking and selecting group -> New Widget.