Reactor Period:
Reactor period is described as that amount of time, generally in seconds, needed for neutron flux (power) to change through a factor of e, or 2.718.
Decades Per Minute (DPM)
Rate circuits are significant in the source and intermediate ranges. Rate information is shown on a meter in decades per minute. These meters denote how fast reactor power is changing in decades (power of 10) in every minute.