Re: Half Adjust

[Hans Boldt <boldt@xxxxxxxxxx>]

Buck wrote:
> > I am using the H for half adjust, when doing a DIV
> > by 100, but I end up being off.
>
> This is how numbers work in computers.  There is a finite number of decimal
> places to which a calculation will be carried, and all those tiny losses at
> the end of the fractional numbers add up in the end.  You can increase your
> decimal precision to minimise the issue, but that will not eliminate it.
>
> There are several answers to the issue.  Perhaps the most expedient would be
> to place a note on the report/display explaining that the numbers don't add
> up to 100 due to rounding.  Or simply print 100% rather than calculate it.
> This would almost certainly take the fewest lines of code to implement.
>
> Another possibility is to keep a running total of the fractional amounts and
> when you get to the last entry, subtract that from the total (100) and use
> the subtracted difference rather than to calculate the last percentage by
> division.
>
>                  trunc
>           1   .0588
>           7   .4117
>           6   .3529
>           3   .1764
> Total 17  .9998
> Adjust final entry by subtracting running total from desired total (1.0000 -
> .9998 = .0002)  Add .0002 to .1764 and print that.
>
> This method is expedient but may result in quite a large mis-statement
> (percentage wise) of the true value of the last entry.  An alternative is to
> perform the same manipulation, but apply it to the largest entry in the
> list, thus minimising the percentage effect of the rounding on any
> individual entry in the list.
>
> In the above example, you would add the .0002 to .4117 instead of .1764,
> thus distributing the rounding error to the value which can absorb it
> easiest.
>   --buck

Good ideas. But the original poster should probably talk to his 
corporate accountants or auditors to find out how the rounding errors 
should be handled. In some jurisdictions, the rules are defined by law.

Cheers! Hans