No! That's how it's supposed to be. You're not measuring the ambient temperature, but the thermocouple cold junction temperature.
A thermocouple generates voltage based on the temperature gradient between the hot side and the cold side.
It has 2 different metals. Those metals go all the way from the sensing tip until the end of the probe.
The temperature gradient ends where it reaches the connector (When the material changes).
Actually, it makes a second TC in series, luckly copper and solder generate little to nothing.
It gets really really complex when you dive into it!
Optimally that junction should be at 0ºC for best performance, no compensation would be required.
Since it's impossible to achieve that in a lot of applications, you must compensate somehow... And that's why the NTC is there!
The TC will either output nothing or negative values if the hot side is colder than the cold side.
In this case, we can only read positive values. So if the junction is at 40ºC, any measurement will be over that temperature.
Of course, it will drif a bit. There are a lot of complex mathematics behind a compensation algorithm, which I'm not doing.
As I said before, this is a soldering station, not a a bio genetics laboratory. 5ºC off are completely acceptable.
Read a bit about thermocouple cold Junction compensation!
![Popcorn :popcorn:](https://www.eevblog.com/forum/Smileys/default/EatingPopcorn.jpg.pagespeed.ce.yJ6TmC5fSa.jpg)
Otherwise, why the *** would the station care about the ambient temperature? Just a fancy reading?
![Face Palm :palm:](https://www.eevblog.com/forum/Smileys/default/xfacepalm.gif.pagespeed.ic.EBDwh1hCfo.png)
I modded my Quicko and moved the sensor to the handle to make exactly that!
I'm going to start saying a famous quote in the developing community, "use it or change it".
That means exactly that, when something doesn't cover your needs or likes, fork it and make your own!
Don't like the font? Don't like the interface? Can't live with a 3ºC error? Change it! Or contribute to the project!
![ThumbsUp :-+](https://www.eevblog.com/forum/Smileys/default/icon_smile_thumbsup.gif.pagespeed.ce._JElyJQqdB.gif)