It was in a C150 Aerobat without a 'g' meter.
As SquawkModeA said, I made sure that the floating objects did not move towards and then stick to the roof as an indication of the level of acceleration. Also there was no force being provided by the lap straps.
It's a fair point that a 'g' meter would have been better but as I don't think the maneouvre when entered progressively causes negative 'g' it isn't needed.
That was the point of the question to confirm my own understanding of the dynamics of the manoeuvre.
I am sure an aerobat experiences more extreme forces than this when doing aerobatic training.
FIS.