I placed 3 qts of water and a thermocouple datalogger in the oven over the past couple days to see if an oven could hold a stable temperature. The water's heat capacity certainly helps to smooth out the fluctuations, but I didn't realize how much. This is just an excerpt of many hours of evaluation, but wow, it's pretty darn stable. I was also surprised how much lower the temp of the water was compared to the atmosphere inside, must be the inefficiency in heat transfer? Whatever, looks good enough to plan a big slab o steak!
Given the length of time required to equilibrate this system, it's lame compared to any circulator, but still a fun observation and good for intermittent use.