As long as you have a good atty and a really stable coil between the post screws, then the coil's resistance will ONLY vary based on the temperature of the room. And even if that happens, it doesn't affect anything because the mod always uses your locked resistance as the baseline. (Some mods don't have resistance lock and that's another issue all together -- some deal with it better than others).
The algorithms these mods use are based on a baseline temperature of 20°C (68°F) because that's the temperature that the industrial spec sheets use as the baseline (i.e. spec sheets like
this one). So the mod is assuming that when you lock in the resistance that the ambient temp is 68°F. If the temp in your house is close to that (say within 5-10F), then the resulting temp should be pretty close to what you set it.
I currently have a 45 ohm single Ti coil in my Derringer. I somewhat indirectly measured the peak resistance it hit with the mod set to 500F by taking a very long series of vapes, and then quickly unscrewing and rescrewing the atty. Thus giving me a real time temp reading from the EVIC (it would be nice if they showed the measured temp while the fire button is pressed but they don't). I get about 62 ohms.
That is a delta of 0.17 ohms over a range of 430F. Dividing, that's 25 ohms per 0.01 ohm. If the atty drifts by 0.02 ohms, which I see very typically over the course of a day or at least over a few days, that offsets the temperature by 50F. So someone comparing a vape at 400F against someone else at 450F or against his own vape the following day, might see identical results.
As long as that resistance remains stable the vape will be fine. The mod might be set to 400F or 450F, giving the same actual vaping results. But if the mod drifts 0.02 ohm in between resistance locks (assuming as you mention that the mod provides for that) then the vape can change considerably.
"As long as you have a good atty and a really stable coil between the post screws"
Sure, it's easy to make an idealized assumption but that is a huge IF. Which has been the point I've been trying to make. I can only speak from experience that among the 3 atty's I now have configured for TC, a 0.02 ohm drift is very typical. I'm happy if that is the extent of it. And in reading many TC threads, I see that I am not alone although in many cases people do not quite understand what is going on, and/or how sensitive that temp measurement really is (in the order of 25F/0.01 ohm).
"And even if that happens, it doesn't affect anything because the mod always uses your locked resistance as the baseline."
Again, that is only true if the circuit remains ideally stable subsequent to locking (either manually or however the device divines that). But in all cases it does affect the vape based on the indicated temp. So if someone gets it in their head that they want to vape at 400F they may be unhappy at times (and I've seen that reported in threads, when people complain about TC problems). And of course, it could be more than 50F. I've seen variances of 100F from time to time. Particularly with new coils that perhaps have not "settled in" yet, or perhaps weren't given quite enough cool down time when a lock reset was needed. Or perhaps who knows
