Using functions

[HSalim]

Hi All.
My report is based off a a query.
Query1: Select ItemNumber, TrackNum from Tracking
in some cases TrackNum = ""

Function:
Public Function Tracking (data as string) as string
' some code for example
strtemp = data & "ABC"
Tracking = strTemp
End Function

now the report uses this function in a control source
Text box control source = Tracking(TrackNum)

One would expect that the fuction is called every for every record.
However, I am finding that the function is called only when Tracknum <> ""
i.e. if tracknum is blank, the function is not called at all.

Any idea why?

However, when I use the function in a query, say
Select ItemNumber, TrackNum, Tracking(TrackNum) as Test from Tracking the
function is called everytime.

Any insight would be most welcome.

Thanks and regards
Habib