OK, that's a bit triumphalist. Sorry. But I've been arguing, at WUWT and elsewhere, about why adjustment of USHCN is necessary. And I get a chorus of - no you can't alter original data, not if it increases the trend. And I point in vain to my earlier analytic justifications for TOBS (here and here). See Zeke for context, and Victor Venema for a much fuller explanation of min/max thermometers and TOBS.
I think I eventually worked out the right counter, so I thought I'd write it down here before I forget.
- The min/max data that you see in a record is not (usually) original data of daily min/max. It is typically a record of the location of min/max markers on a thermometer at a specific time of day (when it was then reset).
- An assumption must then be made to connect that with records of specific days. In the old style, you might assume that a max marker at 5pm Tuesday (example) was the daily max for Tuesday. If it was at 9am, you'd assume it was the max for Monday (and at some time in between, you'd have to switch).
- Repeat, this is an assumption. It is not original data. And it won't always be right. Many of those 5pm Tuesday readings would have been set the previous Monday. That would arise from a warm afternoon when 5pm, not the max for Monday, was warmer than all of Tuesday to 5pm.
- This is double counting, and 5pm creates a warm bias. Warm afternoons can get counted twice. Cold mornings don't.
- Repeating again, an assumption was made and is inevitable. It creates a bias. People raised objections about how the bias can't be measured exactly. I emphasised here that there was a huge amount of data to base an estimate on; that the analysis was straightforward. Oh no, they say, how do you know that people actually read when they said they did (answer - see DeGaetano in that link). Etc. But anyway, the key thing is there is a bias, and it's a scientific duty to estimate and allow for its effect. The objectors want to say it is zero. That's an estimate, baseless and bad. We can do much better.
- The original data is not data about daily temperatures. To get that requires interpretation. And you have to do it right. Laziness won't wash. We can do better. Over the years, NOAA has done better. And yes, for reasons explained in link above, that had a warming effect.