Accurate and precise enough for me!
I got the TP509 to use when making fudge, which needs a fairly accurate and precise reading, to replace other thermometers which had worn out or gone out of spec. Initial impressions: I like the long stem, which gets the reading out of the steam. The numbers are large and easy to read, and the tilting head means I can read it comfortably.I put this in a pan of water (filtered but not distilled) and brought it to a boil and set the thermometer's height to not quite touch the bottom of the pan. For the first test, I only put in enough water to cover the thin part of the tip of the probe, and brought it to a full rolling boil. The reading was about 210F. While it was heating, I noted that the reading increased in steps of 0.3F to 0.5F at a time, and updated every 1-3 seconds.Next I added more water to triple its depth and fully submerse the tip. At a full rolling boil, the reading was mostly 210.9. Not quite 212 but I remembered about altitude. At my altitude, the boiling point of water is about 211F so I'm calling that accurate :-)While it was nearing a boil, I did stir the water a bit to make sure the reading was appropriate, and noted that I could see the reading fluctuate - it was capturing the hotter and colder portions of the water!After the water cooled to 160F or so, and thus the reading was changing much slower, I noted the steps it was using. The reading was changing between 0.3F and 0.5F per step, or on the C setting, 0.2C to 0.3C per step. I assume this means the device is converting between the internal ADC numbers and the desired temperature unit, and not converting to C and then to F and losing precision.The clip was easy to use and fit my pans nicely, but I'll add the usual warning of "hot things are hot" so get the height right before you turn the heat on.For yuks, I put my old digital thermometer in the pan too - this was a pampered chef model with an off-brand replacement probe (the original probe was more accurate until it broke). It bounced between 214F and 216F (yes, that's a 2F step). This is why I needed a new thermometer ;-)