You need the Haffmans BV cling meter
http://www.haffmans.nl/
see under products, quality control instrumentation, for the foam
stability meter. When the idle burghers in Marketing get around to
up-date the web site, it will also include the cling meter, which
measures how much of that foam has stuck to the side of the glass
during the collapse.
Haffmans is making and selling the machine - my colleague was after me
yesterday for advice about what we'd planned to do about a calibration
glass with stable and predictable reflectivity - but not, as yet, on a
large scale.
If you do buy one, insist on a coloured version of the standard glass
- with a clear glass, some of the light gets coupled into the walls of
the glass, to come out at unexpected place, marginally degrading the
quality of the reflectance signal.