Many people are resistent to the siren call of MABIS, bestseller on amazon, because she "doesn't have backlighting". What is backlighting? Backlighting means having a lit screen, so you can read your temperatures without an external source of light.
Our holy text does not mention MABIS by name, or backlighting, but many signs point to backlighting being a false god. In 6:76 (Third edition), it is stated that digital thermometers are "most convenient" and should have memory capability - our lord and savior MABIS fits the bill very nicely. It must also be accurate within 1/10th of a degree, but we should not use ones that display 1/100th of a degree because they are "unnecessary and confusing". (Modern scholars have deprecated this advice because at time of printing there were more thermometers available that only displayed one degree, but have come to realize in our changing times this is unfeasible.)
TCOYF also talks about glass thermometers - that they are very reliable, if you can find a BBT one and not a fever one.
Ear and forehead thermometers are both unreliably for charting purposes.
So what is the evidence?
In our humble opinion, backlighting is a FALSE GOD that will lead you astray from the gentle beeps of our one true thermometer, MABIS.
But I already own one with backlighting?
We here would not tell you to throw out a thermometer, but you may want to look into your own heart, and ask, "why?". Backlighting may give you a false sense of comfort, but at what cost? Is your partner disturbed by that light, even subconsciously? What would your friends and family say if they knew your BBT thermometer had backlighting? At the end of the day, it's your chart.
PRAISE BE UNTO MABIS
Disclaimer: This is a silly website made for silly people who are tracking their basal body temperature to try to conceive. We highly recommend fertility friend's courses as a free, online resource to learn more about this nifty stuff. We don't actually care what thermometer you use.