Hey Doc,
I'm glad I came across your post. A few nights back I brewed a partial version of Boonies LCPA and used a 26L esky as a mash tun for the first time. Until then I did my partials a la stove top in a pot - improvisation by necessity. Anyway, using a standard glass thermometer, I was stunned at the temperature gradient from the bottom of the tun to the top. There was a temperature change of 5C or so, with a low temp at the bottom and hi temp at the top. The observation caused a bit of a panic on my part. Without much experience to fall back on, I was unsure where exactly to place the thermometer and subsequently add either boiling or cold water to adjust the mash temperature.
At first I wondered whether I was getting too much heat loss from the mash tun, but ruled that out pretty much. And I was reasonably confident in my procedures. So I've put my mind at rest, reminding myself that the laws of physics at play in my mash tun are the same as in everyone else's mash tun.
Now, as an engineer, I'm all for accuracy. But accuracy in temperature measurement becomes far less meaningful unless we're consistent in terms of where in the mash tun we take a measurement, I would think. My inclination would be to take a reading from the middle of the mash (that's what I did the other night) as an indicator of average mash temperature. But I'm all ears.
As long as I'm not hijacking this post, would love to hear what others do? I just think the point of temperature measurement is at least as important as having a you-beaut thermometer.
Cheers