A Servomex is a paramagnetic oxygen analyzer. It is used to tell you what your gas identity is and the strength/purity of that gas. A Servomex's accuracy is ±0.1% Oxygen and has been validated
by ORSAT apparatus to USFDA Pharmacopoeia 23.

Oxygen is magnetic! Oxygen is attracted to a strong magnetic field — most other gases are not. This para-magnetism is used to obtain fast, accurate measurements.

If your oxygen analyzer reading is 99.5%, then your oxygen is between 99.4% and 99.6% pure.
 

Why can't I use my handheld analyzer when testing the identity and purity of my gas?

A handheld analyzer uses fuel cell sensors which are much less accurate — ±3.0%. This means that your 99.5% oxygen could be anywhere from 96.5% and 100% pure (possibly not Oxygen USP)! Therefore, the FDA has specified using a paramagnetic analyzer, such as a Servomex.