Paul.
an x-girlfriend of mine was a big wig in the UK Kirby business, in the beginning when she was just getting started she practiced her demo in front of me ( I must have seen it 100s of times). part of the demonstration was this sugar & flour test. She rubbed it into the floor and asked the customer to us their existing vac and vac it all up, then she would pull the Kirby once across the test area.
The Kirby was fitted with a inspection chamber instead of the cloth bag, she would empty the container and show the customer how much their vacuum had failed to pick up.
It was a very persuasive test, the Kirby always removed more sugar & flour.
but this was against normal domestic vacs.
Mike