Data logger and sampling and encoding methods for use in a data logger

A data logger for logging values of a physical environment parameter (T) as a function of time (t) includes a sampling subsystem, which acquires sample values of the physical environment parameter (T) at sampling moments which are separated by sample intervals, an encoding subsystem which defines data records representing groups of one sample value or a number of successive sample values with variations which meet a first stability criterion, each data record including first identifiable bits (b-b) defining a representative value (Trep) for the samples values of the corresponding group and second identifiable bits (b-b) indicating the number of samples in the corresponding group and a flag bit (b) indicating the use of either the first or second interval length, and a memory subsystem for storing the sequence of defined data records into a memory.