I use a Fluke Model 16 digital multimeter with thermocouple. Yes, it's overkill, but I had the meter around for electrical test purposes anyway. It costs around $100.00 or so, which is more than I would pay for a darkroom thermometer. However, it reads temperatures to a tenth of a degree, and reads a good stable temperature less than a second after being immersed in water. It's by far the best thermometer I've used. It's also a really wonderful voltmeter.(posted 8339 days ago)The thermocouple may not take kindly to long-term exposure to photochemicals, but I rarely use it for anything but water baths or water out of the tap. If it corrodes, the sensor is very cheap to replace.