Predicting O2 meter reading:

  1. Multiply vapor pressure (of known material) times 1300 to find maximum achievable PPM.

  2. Divide PPM by 50,000 to get predicted drop. [The reverse of multiplying times 5, and then multiplying times 10,000 (O2 is 1/5 of air) used in the “Understanding Meter Readings” section to get PPM]

  3. Subtract the predicted drop from 20.9%, this will give predicted meter reading.

Example: Known chemicals vp is 15.4mmHg

15.4 x 1300 = 20,020 ÷ 50,000 = 0.4%: 20.9% – 0.4% is 20.5% predicted meter reading