I have written a function that I am calling from a query to calculate what I
call a "precision index" (PI).  I have recordsets of different sizes, but I
only want to calculate a PI on recordsets with a record count of 3.

I have tried inserting code to the effect of:
if Recordcount <> 3 then
P=0
.nextrecordset

But I get the error message  "operation is not supported for this type of
object"

My function is as follows:

'function to calculate precision index on tooth ages by sample_ID and Reader

Function P(Age As String, Reading_Number As String, tblAges As String,
Optional WhereClause As String = "" _
) As Single

Dim dbPI As DAO.Database
Dim rsPI As DAO.Recordset
Dim strsql As String
Dim rcount As String
Dim firstage As String
Dim secondage As String
Dim thirdage As String
Dim PI As Double

Set dbPI = CurrentDb()
strsql = "select [" & Age & "],[" & Reading_Number & "] FROM [" & tblAges & "]
"
   strsql = strsql & "WHERE[" & Age & "] IS NOT NULL "
       If Len(WhereClause) > 0 Then
       strsql = strsql & "AND (" & WhereClause & ") "
       End If
       strsql = strsql & "ORDER BY [" & Reading_Number & "]"

Set rsPI = dbPI.OpenRecordset(strsql)
If rsPI.EOF = False Then
   rsPI.MoveLast
   End If
   rcount = rsPI.RecordCount

   If rcount <> 3 Then
   rsPI.NextRecordset
   End If
         
rsPI.FindFirst (Reading_Number = "1")
firstage = rsPI("age")
rsPI.MoveNext
secondage = rsPI("age")
rsPI.MoveNext
thirdage = rsPI("age")

If firstage = secondage And secondage = thirdage Then
   P = 1
  ElseIf firstage = secondage And secondage <> thirdage Or firstage <>
secondage _
   And secondage = thirdage Or firstage = thirdage Then
   P = 2
  ElseIf firstage <> secondage And secondage <> thirdage Then
   P = 3
End If

End Function

If the record count is <> 3 I would like to set P = 0 and move to the next
recordset.  If the record count = 3 I would like to calculate a PI based on
the rules defined.

Any suggestions would be appreciated.
Any suggestions