What exactly does TC precision entail? Is a higher value more desirable, or lower?
The TC precision number in the Wire Wizard is an attempt to describe how easily a mod can sense the temperature of a coil. A higher number means that you should have more precise temperature control.
The number is the product of the two most important factors for temperature control; the TCR and the base resistance. It is calculated by multiplying TCR * R * 1.000.000.
To expain the reasoning behind this calculation, let me first give you a technical fact, which is true for all electronics:
As long as the resistance is not too low, it is easy to measure it with reasonable accuracy. But if the resistance gets too low, accuracy goes out the window, unless you start employing some special techniques, like four terminal sensing. Mods don’t have the hardware for this.
Here are two practical examples from temp control coil building:
Ni200 has a very high TCR, which is good. This should make it easier to measure the change in resistance. At the same time, Ni200 has a very low base resistance, which makes it hard to measure the resistance accurately to begin with.
Titanium, on the other hand, has a lower TCR. It also has a much higher resistivity, which gives the coil a higher base resistance. As the temperature rises, the resistance does not change as much in relative terms, but because of the higher base resistance, the absolute change in resistance is still significant.
So: When the mod has a larger cold resistance to calibrate to, and a larger absolute resistance range to work with, all the internal resistances (of the mod itself, the 510 connection, the atomizer, and the coil post connections), will become less significant, and contribute less error.
In principle, this should – potentially – lead to a more precise temperature control. And that’s what the TC precision number is an attempt to convey.
By the way, the only purpose of the factor of 1.000.000 is to bring the number up to an easily readable range.