Thermo Scientific APEX 100 User Manual page 366

Key
M = Machine parameter. A global parameter that defines the underlying
operation of the detector—such as model type (100, 300, 500),
application used (conveyor, gravity-feed, pipeline, or Rx), and the
preferred units of measure (feet or meters).
P = Product parameter. Any product-related parameter—such as product
name, phase angle, and so on.
RO Read-only register
R/W Read/write register
For other abbreviations and acronyms, see the Glossary at the end of the manual.
Thermo Scientific APEX User's Guide Page 366