Re: PDF File Size using FM6 and Acrobat 3.05

[Michael Cudmore <mcudmore@xxxxxxxxxxx>]

Dan Emory wrote:
> So,  in cases where you're calculating a percentage difference
> between two numbers, neither of which is "the whole," it
> seems more fitting to define the ratio as follows:
> 
> Let A and B be two numbers, where A is the larger number, thus:
> 
> P = (A - B)/B x 100
> 

Whether or not the percentage relates part and whole is not the issue. 

When you calculate a percentage, in general you are taking a fraction
of a value over a base value and multiplying by 100. The two numbers
may not be related as part and whole, or old and new. In this general
case, you might talk of the Australian population being 8% of the size
of the US population; in other words, you explicitly refer to the base
value. 

When the percentage is a percentage change or difference (e.g. part
compared to whole or new compared to old), you need to compare the
difference (new minus old or part minus whole) with the base value
(old or whole) before multiplying by 100. But when talking about
percentage changes, the base value is left implicit; you simply refer
to the percentage change in file size, rather than the change in file
size as a percentage of the old file size. You do not need to state
the base because there is only one sensible value to take as the base.
In particular, the base is not chosen on the basis of which number A
or B is larger.

The percentage change between old and new is ALWAYS 

    (new - old)/old * 100

This formula applies whether you are talking about whole and part, old
and new, etc. In your PDF  case, (300 - 1200)/1200 * 100 = -75%. The
negative sign indicates, as it always does if this formula is used
correctly, that the change is a reduction. 

I don't really understand why I need to go through this. It's not
April fools' day is it? The new value is a quarter of the original
value, so it must have been reduced by three quarters, or 75%, of the
original. There is simply no other sensible way to express
percentages. Sheesh, if folks go around saying it is OK to redefine
percentages, it is no wonder percentages and probabilities can be
confusing to otherwise intelligent people. 

To finish, a mathematician's urban myth:
In the 1970s, the Mexican roads department decided to repaint the
lanes on a 4 lane highway to give 6 narrower lanes. It then claimed to
have increased lanes by 50%. After accident rates soared, it went back
to the original 4 lanes and reasoned that following a 50% increase and
a 33.3% reduction, it had still managed to increase the number of
lanes by 16.7%. 

cheers

--
Michael Cudmore
Project Development Manager
National Educational Advancement Programs (NEAP) Pty Ltd
58 Pelham St  Carlton  Vic  3053   AUSTRALIA
Tel:    +61 3 9663 2523    Fax:  +61 3 9663 7182
e-mail: (work)    mcudmore@neap.com.au
        (pers)    mcudmore@email.com

** To unsubscribe, send a message to majordomo@omsys.com **
** with "unsubscribe framers" (no quotes) in the body.   **