gunson gastester

[bagodoosh]

for those with experience with the gunson gastester, or any 1 channel CO measuring device:

what's your sequence of operation:
do you use 1 exhaust connector or two? (part# 88713.1010 union for exhaust)
does it matter if you leave the other side open during testing?

on the side,
what do you think of the gunson being calibrated to 2.0% ?
the CO level should be 0%.
as a reference, UL2034 standard specifies that a residential CO detector should alarm if 400 ppm is detected between 4-15min. that is .04%, which can cause death after 2 hours. .01% can cause headaches after 4 hours. they are claiming 0 calibration is 2%!

in their adjustment procedure they state:

Note: 2.0% is the background level for CO2 in the atmosphere

so the device is measuring CO, but they are calibrating to CO2 levels? 

any technical input?