> Scott wrote:
>  > Comparing to last year/month is pointless,
>
> It makes sense in a seasonal business.

Not really, because it's comparing your current performance with one 
arbitrary data point.  It can give a very misleading figure about 
actually how well you are doing, either due to random variation in the 
figures, or that you just had an exceptionally good/bad figure the year 
before for some reason.  It only tells you one thing, yet people try to 
draw far more conclusions from that one figure.  A simple chart of even 
just 10 data points is infinitely better.

Real world example, my sister manages a shop (which has very seasonal 
sales figures) and just after she started the job she kept getting "best 
in region" month after month.  She couldn't really understand why, until 
she figured out that they were simply comparing her monthly sales with 
12 months ago, where the store had been run by someone with no 
motivation and who wanted to leave.  Now she doesn't get "best in 
region" very often (it's probably mostly random variation between shops 
if all the managers are relatively competent).

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