Activity monitoring systems and methods of operating same

An activity monitoring system comprising:

• a first fixture having (i) a physical size and shape that is adapted to couple to an associated location on the body of the user and (ii) a particular signature;
• a portable monitoring device adapted to physically engage the first fixture and to detect the particular signature of the first fixture, the portable monitoring device including:
• a housing having a physical size and shape that is adapted to couple to the body of the user and to physically engage the first fixture when the first fixture is coupled to the associated location on the body of the user;
• an activity sensor, disposed in the housing, to detect activity of the user and, in response thereto, to generate data which is representative of the activity of the user;
• and
• processing circuitry, disposed in the housing and coupled to the activity sensor, to calculate one or more activity-related quantities of the user using the data which is representative of the activity of the user, wherein the processing circuitry:
• determines the portable monitoring device is physically engaging the first fixture based on detecting the particular signature associated with the first fixture, and,
• in response thereto, calculates an activity-related quantity of the user which is associated with the first fixture using data from the activity sensor.