What do you want to happen when one or both of the end points are
missing? You can use the Nz() function to deal with null values on either
size of the equation by converting them to actual numerical values. Maybe:
Nz(EndPoint, 0) - Nz(StartPoint, 0)
However, with that you might end up with bad lengths. So if EndPoint is
35 and there is no StartPoint, you end up with 35. Or with the reverse you
end up with -35. If the lack of an end point indicates less than a mile,
perhaps:
Nz(EndPoint, Nz(StartPoint, 0)) - Nz(StartPoint, Nz(EndPoint, 0))
This would use the start point when there is no end point and the end
point when there is no start point. If neither point is there, it just uses
0 - 0 which results in 0.
Hope that helps,
Clifford Bass
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Message posted via AccessMonster.com
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Further, you may want to use the Abs() function so you always get
positive numbers:
Abs(Nz(...) - Nz(....))
Clifford Bass