but now that you mention that, it's all coming back. Weren't they using a differential pressure guage rigged in a coffee-can type setup, when it should have been an atmospheric pressure guage? That would continue to read 0 psi (which they assumed to be field elevation) while they pressurized the cabin. Since they were expecting the pressure to go up, and the guage kept reading 0 psi, they kept adding more pressure until the balloon popped!