Picture a two channel colorimeter in the infrarad and red, with a
bargraph display, and two digital readouts of two digits each. How much
would a thing like that cost?
$25, when sold as a pulse oximeter - a gadget that clips gently over
your finger nail, and which measures percent saturation of arterial
blood with oxygen, and which provides a pulse rate measure too.
I bought one on impulse, via internet of course. An opportunity for
portraying deviation and mean values?