A running record kept as things happen. Its worth is that it was written at the time and not reconstructed after.
Middle English logge (a bulky piece of wood, a felled tree trunk), of obscure origin, perhaps Scandinavian; sailors towed a log on a line to gauge a ship's speed, and the record of those readings became the log — a running record kept at the time, not reconstructed after.
The house's memory of what actually happened, kept in the moment rather than assembled afterward from memory alone — closer to the sailor's towed line than to a diary.