For a user using Imperial units, typically, when creating drawings/layers the variables will automatically be set to use Imperial Expressions and the Windows decimal separator in use (either '.' or ',').
So then, expressions such as w + 0.5 or w + 1/4 will be interpreted as 0.5inch and 1/4inch.
When this option is enabled, if a drawing containing such expressions is opened by a user running in Metric units, the expressions will still be evaluated in Imperial units. However, the variable values displayed in the explorer will be in metric using the users configured units formatting.
If you have set this option and it causes a mismatch with your default settings this will be highlighted at the bottom of the Variables tab:
