Create a combo box using the wizard, and have it take unique values from the table that has this parameter column. I'll assume the column name is SubUnit.
If your report is based on a query, then add this to the SubUnit column Criteria line in the query designer:
Then EVERY time you open the report, it will look for the combo box, take the selected value, and open the report with only those subunits.
If you want the report to run without criteria, then you can either create a copy of the report just for sub units and create a copy of the query just for sub units with this criteria and open that when someone wants the sub units, and open your current report when they want all the info.
Alternatively, on the button to open the report (same report as current) where the user selects criteria, then just do this:
Dim sUnit As String
Dim sLink As String
Dim sDoc As String
sDoc = "rptMyCurrentReport"
sUnit = Me.cboSubUnitComboBox
sLink = "[SubUnit] = '" & sUnit & "'"
DoCmd.Open Report sDoc, , , sLink
The sLink variable should be in the WHERE clause section of the DoCmd line. You may also want to check to validate a selection.
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