Look into time-series compression. Delta-encoding, mentioned by sibling, is a very old but effective technique also known as differential PCM. You can also delta-encode delta-encoded values, which works especially well for values whose delta is constant (classic example: timestamped data). The advantage of these over general purpose compressors is that they require basically no resources to implement. TFA is "low memory usage (as low as 50 bytes)", but delta encoding needs just one register.