Reading some documentation gives me a slight idea of millis(). Here goes.
If let's say the Rx detects Tx at 4500ms, but has been running for 4000ms, 4500 will be the value of latestMessageMillis, right? That number will then be subtracted by how long the Rx has been running to show the delay, correct?
Just saying what I see it does to make you see if I understand it.
But for the sake of improving my programming skills, how can I make my code work? I thought that adding the delay allows the variable to increment 10 per 10ms...