Honeywell ACM 150 Manual To Installation, Operation, And Maintenance page 151

ACM 150
PSIA
Pounds per square inch absolute, pressure relative to a vacuum.
PSIG
Pounds per square inch gauge, pressure relative to atmospheric pressure at sea
level.
PPM
The ACM 150 monitor reports concentration values for gases in parts per million
(PPM) and parts per hundred thousand (PPHT) (water vapor only).
A pure gas would have a value of 100% concentration (by volume). One part in
one million (1 PPM) is 0.0001% or 100% divided by 1 million. 1 PPHT = 10 PPM.
These are the relationships between PPB, PPM and %:
PPM
0.01
0.1
1
10
1,000
1 million 100.0
TLV
Threshold limit value
TWA
Time-weighted average
%
0.000001
0.00001
0.0001
0.001
0.1
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