Commenting Help

A buddy of mine wrote this code and i am needing some help to understand it...you guys able to help me out?? or comment some of it? thanks, oh and if you feel something should be changed let me know



Private Function GetFeedDisappearance(ByVal lngdropID As Long, sngPeriodLength As Single) As Single
Dim strSQL As String
Dim strDateSQL As String
strSQL = "SELECT DropDateTime FROM DropHistory" _
& " WHERE DropFull = True AND DropID = " & CStr(lngdropID) _
& " ORDER BY DropDateTime DESC"
With rsTemp
.Open strSQL, cnMain, adOpenForwardOnly, adLockReadOnly, adCmdText
If .BOF And .EOF Then
mdtmLastDate = 0
GetFeedDisappearance = 0
mdtmFirstDate = 0
msngTotalFeedUsage = 0
msngUsagePeriod = 0
.Close
Exit Function
Else
mdtmLastDate = !DropDateTime
mdtmFirstDate = !DropDateTime
Do
.MoveNext
If .EOF Then
GetFeedDisappearance = 0
mdtmFirstDate = 0
msngTotalFeedUsage = 0
msngUsagePeriod = 0
.Close
Exit Function
Else
mdtmFirstDate = !DropDateTime
End If
Loop Until (mdtmLastDate - mdtmFirstDate) > sngPeriodLength
End If
.Close
End With
strDateSQL = " WHERE DropDateTime > #" & CStr(mdtmFirstDate) _
& "# AND DropDateTime <= #" & CStr(mdtmLastDate) & "#"
strSQL = "SELECT SUM(TotalByWeight) FROM DropHistory" & strDateSQL _
& " AND DropID = " & CStr(lngdropID)
With rsTemp
.Open strSQL, cnMain, adOpenForwardOnly, adLockReadOnly, adCmdText
msngTotalFeedUsage = rsTemp(0).Value
.Close
End With
msngUsagePeriod = mdtmLastDate - mdtmFirstDate
GetFeedDisappearance = msngTotalFeedUsage / msngUsagePeriod

I try my best to help u!This is my expaining for this code:
At the first:
run sql statement to find some recordsets that have DropFull = True AND DropID = " & CStr(lngdropID)..

If can't find any recordset in the db,it will have two error like EOF and BOF.The function will return some result variables as:mdtmLastDate = 0
GetFeedDisappearance = 0
mdtmFirstDate = 0
msngTotalFeedUsage = 0
msngUsagePeriod = 0
And Close the sql connecttion,Exit function;

Comment:
BOF returns a value that indicates whether the current record position is before the first record in a Recordset object.
EOF returns a value that indicates whether the current record position is after the last record in a Recordset object.

2th:if find EOF,then have no recordset according with having "DropFull = True AND DropID = " & CStr(lngdropID) ".The function will return some result,close the connection.

3rd:find some recordsets according with the condition,the function will get the SUM of the(TotalByWeight) between the mdtmLastDate and mdtmFirstDate,calculate some result to return...