Well by definition your weight DO change, but your mass doesn't.
SImple test: Stand on a scale and raise your arms fast as you look at
the scale, it will indicate your wight increases. That is what it measures,
not your mass, which is constant.
I was impressed when I saw it on TV, very cool but prolly not easy to duplicate ;)

You need a very sensitive scale that can detect the total weight and also 
handle the small delta weight measurments. Also some digital filtering
to get the pulse from the signal.... DSP ?



> To be picky a little here - I'd think your weight doesn't change there.
> Your body probably moves a little though, in response to the pressure
> change when your heart beats - and that's what they measure;  your
> inertia's effected by the pulse, and oscillates <G>  Interesting info!
> 
> Same effect as if you drop a hammer in an airplane - You can NOT use the
> oscillation of measured weight as an antigravity drive AFAIK, you CAN
> measure the change to tell that the hammer's been dropped, though...
>   Mark