Int rounding down (calculated) whole numbers

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I have a function during which a line passes a calculation to an integer,
usually all is fine, but occasionally, where the result of the calculation is
a whole number this is also rounded down (eg 12 is rounded down to 11). Note
this does not happen for all whole numbers passed, the two examples I
currently have are 12 and 28.
I suspect the cause of the problem to be in the phasing of the code for the
calculation, perhaps someone could look-it over and make some suggestions?

Background:
A function is required to round times to the nearest x mins (this element
taken as stand-alone works with no errors yet found), however the function
also needs to allow for an off-set:
eg from 7 o'clock the times to the nearest 15 mins are 7:00; 7:15; 7:30; 7:
45; 8:00 etc.
however from 7:10 (time off set by 10 mins) times are: 7:10; 7:25; 7:40; 7:
55; 8:10 etc

My “simple” solution to this is to remove the off-set time; round the the
nearest x mins; then add back the off-set.

Code:

Public Function TimeRoundDown(dteHighTime As Date, _
Optional intNearest As Integer = 60, _
Optional intMinPast As Integer = 0)
'
' This returns the time Rounded Down to the nearest interval
' if no interval is given time is rounded to nearest hour*.
'
' * mins past is used to round to nearest mins past the hour
' eg time of 7:20, rounding nearest 15 for 10 past the hour
' rounded down time is 7:10
'
Dim intTimeBlks As Double
Dim dblStdMin As Double
Dim dblConv As Double

dblStdMin = intMinPast / (24 * 60)
dblConv = 24 * 60 / nz(intNearest, 60)

dteHighTime = dteHighTime - dblStdMin

' Next line causes error:
intTimeBlks = dteHighTime * dblConv
'
TimeRoundDown = (Int(intTimeBlks) / dblConv) + dblStdMin

End Function

Known Problem values:
3:15 to the nearest 15, off-by 15 mins problem line returns 11 not 12
7:15 to the nearest 15, off-by 15 mins problem line returns 27 not 28

Any suggestions gladly received,
Simon

Ps
Access 2007 on XP or Vista pc.

--
Message posted via http://www.accessmonster.com

.

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