Confused by date calc result

[K1200]

This one is right out of the book. I'm simply trying to set a variable to the number of days between two dates. My script step is:

Set Variable [$Diff; Get(Current Date) - Invoice Date]

What I get is $Diff = 179:24:37 ... which equals the days expressed in hours:mins:secs.

What is preventing the calculation from simply returning 7 days or 7.46 days? Is there a better way to calculate days between dates?

Thanks in advance for any help.

[comment]

Is Invoice Date a date field?

Also, what do you use to view the variable?

[K1200]

Thanks, comment. That was the nudge I needed. Upon inspection, Invoice Date is actually a Time Stamp field. I changed the calculation to use GetAsDate(Invoice Date) and it seems to work.