An optical unit capable of freely changing the refractive power and operating with a reduced deterioration in performance, an image taking apparatus having an image taking lens using the optical unit, and an optical finder using the optical unit. A probability estimation module receives the request sequence from the ARQ algorithm and estimates a probability associated with each symbol or bit in the sequence according to a customized Markov model. The monitoring system is particularly adapted for use with inflation garment therapy and negative pressure wound therapy systems. Suspect conditions related to analysis can be identified and appropriate warnings provided.