Ok, so here's a general picture I'm seeing forming with my TCR usage on the Imp:
The baseline instructions of TCR 185 work fine for me with my measured stock coil resistance reading of 222 ohms locked in. Temperatures and vapors feel appropriate for a given temperature. No coil glowing until about 440-445°.
Lowering my TCR seems to have the effect of speeding up the first hit on a cold start. Slight, but noticeable enough to explore. So, for every 20 units of reduction in TCR, I seem to need 8 ohms of resistance increase to keep things in what I consider to be the "realm of reality" and to keep glowing down until 440°.
I'm not going to claim this is truly linear function. I'm sure it's not, but in the ranges I've tested it (105-205 TCR) it holds very true. So these are the values that work for me:
TCR 105 - .254 ohms
TCR 125 - .246 ohms
TCR 145 - .238 ohms
TCR 165 - .230 ohms
TCR 185 - .222 ohms --- stock
TCR 205 - .214 ohms
Since every coil is a little different, I would base your scale on stock TCR 185 = your measured ohms and work out the rest from there.
The difference in heat up times I find is quite different between 105 and 205, with 105 delivering vapor faster from a cold start without nearly so much priming. I'm able to go to a faster, steady draw more quickly with a lower TCR. This is all at the same temps with the same amount of non-glow.
I'd love some verification of this from other users. I'd also like some box mod safety experts to chime in on the safety of this technique. So far in the range I've tested listed above, everything seems to be working as expected. I'm also curious how this might affect battery life. I feel a lot of battery is used (for me) priming cold start hits as I'm a microdoser doing 2-3 hits at a time at most, generally.
Right now rocking some TCR 105 hits and enjoying life immensely. Great, great vape.
Below is copy and pasted from this link. I use the correct cold OHM with DNA chips unlocked. For other mods I'm going let other offer there feelings using this method. Personally I don't feel it's the best method since you can adjust TCR on device.
https://www.ecigssa.co.za/guide-to-fine-tuning-temp-control-vaping.t18206/
I suggest reading the whole post it's a good overview on TC. Below is info that more directly relates.
**TCR gives us how large the change in resistance will be for a change in one °C. For SS 316L, each °C increase from room temperature will give a 0.000879 Ohm change in resistance, for a 1 Ohm coil. For a 0.5 Ohm coil, the change in resistance for each 1 °C will be (0.000879 * 0.5) 0.00044 Ohm; for a 2 Ohm coil, it will be (0.000879 * 2.0) 0.001758 Ohm.
Cold or Nominal Resistance, and resistance locking: Since TC measures the
change in resistance, it is
very important to have a baseline resistance for the mod to use as a calibration of the temperature curve. For almost all TC mods, this baseline resistance is known as the
cold resistance, and is usually defined as the resistance of your coil at room temperature (which is not, for whatever reason, 25 °C but more often 20 °C. Stupid North-centric thinking...). The
nominal resistance of your coil is the resistance of your coil at the current ambient temperature - but generally not something that you have to worry about. You don’t have to cool your atty down to 20 °C when you connect it (unless you have a fancy mod with an ambient temperature sensor, such as a DNA200 - in this case, you will have an absolutely consistent TC curve
if you can connect it at around 20 °C), but you have to make sure that your atty is cooled down entirely.
It is extremely important that when you attach an atty to your mod that the atty is cooled down to the current ambient temperature. Just to give you an indication of the sensitivity we are talking about, consider the following example. You have an SS coil installed, with a resistance of 0.5 Ohm, at the current ambient temperature of 28 °C (your mod will most likely assume it at 20 °C, but the 8 ° difference won’t hurt us much). You take a toot or two on it - and the coil temperature jumps to 240 °C, with a resistance of 0.68 Ohm. If you remove and reconnect your atty (and stating that it is a ‘new coil’ - more on this in the next paragraph), your mod will think the base resistance is 0.68 Ohm at 20 °C. If you hit it now, it will go up to what the mod thinks is 220 °C, but the resistance will be 0.86 Ohm, which in reality will be ~400 °C. In other words, you will get one hell of a dry hit, and most likely some fire from the atty as well. This is a drastic example, but take my word that even a change of 0.05 Ohm of the base resistance can lead to very large (40 to 100 °C) changes in the measured temperature in comparison to the actual temperature. This will either lead to a dry hit when the mod thinks it is still safe, or practically no vapour at all.
Locking your resistance is a bit of a disputed issue. Some people say you say that you should always lock your resistance after installing your coil. I, as well as some others, disagree. In my opinion, you should only lock your resistance if your atty’s resistance tends to fluctuate (for whatever reason), or if you tend to vape in different temperatures (such as in an AC-controlled office, as well as out in the eyes of Hades aka South African sunshine) and you
don’thave a built-in ambient temperature sensor in your mod. Regardless of my or anyone else’s opinions, lock or don’t lock your resistance based on what you feel works for you. Keep the following in mind though: the resistance of a coil takes a number of vapes to settle (and, quite often, only settles after leaving it overnight), and might even change a bit directly after a rewicking. So if you do lock your resistance shortly after a rebuild/rewick, just check the actual resistance a day later to see whether you need to adjust your (locked) resistance. In addition, if you feel that your vape isn’t the same at a given temperature two days in a row (especially near the end of a coil’s lifetime), then you might want to check the locked resistance again. Lastly, if you lock your resistance in order to get a more consistent temperature callibration throughout the day, try to measure and lock your resistance early in the morning, before you start vaping, and keep it locked for the day, but unlock and relock again the next morning. With all that said, I actually tend to lock the resistance of stock TC coils - I found these to sometimes fluctuate a bit.