I would like to sort a group of stocks by the percentage change in the Short Interest (which only updates every 2 weeks and then is sort of backdated to the change date) and or the Short Percentage of Float.  I know when it is updated so that doesn't bother me, but how can I refer to either one in a formula?

thanks for the help, Fred

You can't refer to either in a formula, but you can plot the fundamental on the chart and then add a Rate of Change Percent indicator to the chart.  Change the Data Source of the ROC% indicator to reference the fundamental indicator of interest. You will generally only want to do this for indicators which do not cross zero and use a plain Rate of Change indicator when the Data Source can cross or equal zero.

How to add an indicator to a chart template
How to edit an Indicator
How to change the data source for an Indicator