Can anybody challenge David's claim here?

See the posts above by:
who measured the reduction with a meter
David Hurst who analyzed a transmission curve
Bret (me), who posted transmission curves

Plexiglass blocks UVB and most of UVA. David said only 17% of UVA is transmitted by 2mm plexiglass. My canopy is 4mm thick, twice as thick, and the transmission dies off exponentially with thickness so roughly (0.17)^2 = ..03 = 3% of UVA is transmitted, which matches what measured: very little is transmitted.