Can values from UDF on multiple tabs be displayed on another tab? (Excel 2003)

I have a huge quantity of data coming from a client.
That means I have no control over the format.
There are 2 tabs for each day of the week that I am trying to summarize the data on another tab.
The data requires summing, averaging, min and max calculations. Additionally, the analysis has to ignore cells with no data and bad data (generally "--") which means that I needed to create UDF functions for MIN, MAX. I also had to create one that reads a range and once it locates the maximum in that range, it returns the value from an adjacent cell, using an offset value. I call it MaxAtOffset(rng As Range, offst As Integer)
On each tab, I can get numbers to generate and can summarize each tabs values.
But when I try to bring these values together onto another tab to create my overall summary, the values do not show. Occasionally, some display but when I move off of the tab and come back, they all revert to zero.
I tried making the UDF's in an add-in but that did not help. I added application.volatile to my UDF's but that also did not help.
I have all recalculate check boxes checked in the options dialog box that I know of. And used Ctrl+Alt+F9.

Your MaxAtOffset sounds a lot like an INDEX/MATCH() function. You can mix that with MAX().

=INDEX(Sheet2!$G:$G, MATCH(MAX(Sheet2!$B:$B), Sheet2!$B:$B, 0))

That formula brings over the value from column G that matches the MAX value in column B on Sheet2.

Properly written UDFs won't care what sheet they're on, too.

Perhaps you can show us a workbook where we can SEE your UDF in action and point out how it's doing the wrong thing. Click GO ADVANCED and use the paperclip icon to post up a copy of your workbook.

Here is a subset of the data.
There are four tabs of data and a summary tab.

Each tab represents one day of data, in one direction (Northbound or Southbound) and this subset is only weekend data.
I have 4 weeks of data at 3 locations.

There are a number of hidden rows and columns. The data is collected in 5 minute intervals and the non-hidden area consolidates that into 15 minute intervals. And then, from that, certain hourly data is being extracted, in addition to min and max numbers within the four fifteen minute intervals that make up the hour.

I am going to look into trying to use your example

=INDEX(Sheet2!$G:$G, MATCH(MAX(Sheet2!$B:$B), Sheet2!$B:$B, 0))

in place of my UDF MaxAtOffset but I do not think I can eliminate my other UDF's.

I hope you can offer some solution as my only other alternative seems to be to combine all data to a single sheet and then work everything there.

Note: IMPORTANT FOLLOWUP INFORMATION
I was able to use the Index, Match and MAX functions and also to use Array Functions to eliminate the need for all of my custom functions.

The new max function is : =MAX(IF(ISNUMBER(L51:M54),L51:M54)) (with Ctrl+Shift+Enter to make it an array function)
The new min function is: =MIN(IF(ISNUMBER(L50:M53),IF(L50:M53<>0,L50:M53))) also as an array function.

Finally, and I do this freely and sheepishly - my summary formulas were pointing at the wrong columns. I forgot that they were copied from a tab that had two extra columns in its hidden columns.