Scale for weighing fully laden power wheelchairs

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

I'm helping my dad customize some power wheelchairs  we bought from - u
guessed it - Ebay!   There are serious weight constraints to be considered,
and I find myself in need of a 4 by 4 foot platform scale to, on occasion,
weigh from 50 to 800 lbs.  I went to Google first, but the models I saw were
professional scales costing around $2K.  Yeow!

http://www.google.com/search?q=800+lb+scale

I discovered that there are things called BIA Body Fat Scales that allege to
measure body fat and water content:  "Electrodes built into the Chrome Foot
Pads send a safe electronic signal through the body. Weight, body fat
percentage, and body water percentage are calculated automatically! * * If
you're wearin' a PACEMAKER, don't be usin' a Body Fat Scale! * *  Is this a
hoax?  There seem to hundreds of them listed there.

It's always surprising to see what's for sale on Ebay.  Sorry, I digressed.
I finally found some cheap, serviceable step-on type bathroom scales by the
caselot.

My question is this:  If I took four identical bathroom scales, a 4x4  sheet
or two of 3/4" plywood and attached wood block "feet" at each corner that
would sit on the bathrooms scales, would their readings (assuming each scale
was zeroed out to start) total up to the weight of the object?  After my
knockout gaffe today, I'm looking for a sanity check just to make sure I
haven't overlooked the obvious.  I think it should work and since I have the
plywood, the only cost would be the four scales.

I'm really looking for a load measurement to the nearest 10 and maybe even
20lbs.   Better resolution would be nice, but it's not necessary.  I don't
making walking around to add up the numbers.  If I got scales that had
digital readouts, I might even be able to network them together by tapping
into the display circuitry.  The reality is that the need is so infrequent
that simple visual summation of all four scales isn't a problem.

--
Bobby G.