Dave Dobson wrote:

If forecast=50 and actual=50, then this was 100% accurate.

If forecast=50 and actual=60, then this was not 120% accurate. The value
should be less than 100%, do you see what I mean?


If forecast=50 and actual=60 then you are (actual-forecast)/forecast =
(60-50)/50 = 20% INACCURATE or you deviated from your forecast by 20%
upwards.

If forecast=50 and actual=40 then (actual-forecast)/forecast =
(40-50)/50 = -20%. You deviated from your forecast by 20% downwards.

In both cases you have a percentage over the forecast figure, with a
sign.

Now, all this analysis is if you want to express your deviation w/
respect to your forecast. If you want to examine the forecase w/
respect to the actual figure then the actual figure will have to go to
the denominator.

If forecast=50 and actual=60 then you have (forecast-actual)/actual =
-10/60 = -16.67%. You underestimated actual by 16.67%.
If forecast=50 and actual=40 then you have (forecast-actual)/actual =
10/40 = 25%. You overestimated actual by 25%.

131% (depending on what is in the denominator) can be 31%
overestimation.

I hope this helps.
Kostis