I take a sample as soon as I have all my runnings collected, throw it in the freezer and its around 60 by the time I get my hot break. I can then figure about where I will end up and adjust hops or add sugar or water or whatever with pretty much the full boil to go. And I always get to know my mash efficiency.
Really? I collect a small sample in a big metal spoon, cool it down by blowing on it and take a reading after about 30 seconds on the glass. works great for me but will give you crazy results if you don’t cool first.
I don’t think the tables are inaccurate so much as it’s trying to hit a moving target while the sample cools (and maybe isn’t cooling uniformly at that).