In short, the 3 baselines in comparison is the comparison of how someone responds under 3 conditions, normal everyday conversation, when they're being pressured or accused of something they didn't do, and how they respond when being pressured and/or accused of what they're being accused of.
The ones who say there's 2 base lines in comparison are leaving out the middle one which is really important. They look at how they respond in everyday conversation and how they respond when the subject they're being accused of is brought up. But because you don't know if they respond that way when telling the truth when they feel accused of something they didn't do, you can't tell if those signs they're giving you are signs they are probably lying or if its just how they respond in those situations, even if they're innocent.
Its important to know how they respond under these three conditions because expressions, body language, change in tone, and their reactions in general could be how they react in general or when they're telling the truth while being accused of something. So those "signs" of lying might actually be signs they're not lying.
For example, I'll list some "signs" of lying that are commonly believed amongst average person.
Now a lot of pop psychology will suggest signs of lying are if someone shifts around, or plays with their hands, looks up, shifts eyes, etc. But the problem is that your just listing stuff people do.
I do that in general and there's other people who do it too, they could've had something up with their hands that made them do that, they could've had something going on that made them move like that, they could just not look people in the eyes in general(I usually don't look people in the eyes when I talk to them), they look up or to a certain direction when they think of something, or they saw something. Thats why you can't rely on those.
Now for more realistic determinants of lying:
(But there's never certainty that they're lying, only probability that they're lying because you don't know everything thats going on with them that can cause these reactions)
Getting defensive, change in tone, submissive body language, submissive tone, appearing uncomfortable, panicking, looking scared or worried.
Now those "by themselves don't mean anything" because they're not matched with the person or used to compare how they respond in normal conditions, when they're innocent and telling the truth under pressure, and when they're being accused of the real thing you want to find out. As well as what the situation is at hand, like are they innocent Americans being accused and questioned about being a terrorist at the airport, right after they just waited 2-3 hours in line. People in that situation aren't the happiest at the time thats happening, so being agitated would be normal. (But sadly being angry is a sign of being a terrorist. In my critical thinking class that was brought up as an example of trying to catch a lier that needs to use critical thinking.)
They could be like me and respond with "all" of those under when they're telling the truth when accused of something they didn't do. Yes there's people who respond that way when they're not lying. So how could you tell I was lying if I do that even when I tell the truth?...
Also they could do some or all of those under normal conditions. So it's not really a give away by itself.
Now if they appeared normal under normal conditions, when they're falsely accused or pressured about something, they keep their cool , or appear confused, or just give a different reaction, but when they're accused of the actual act they get mad and defensive, or show signs of panicking, or just completely react differently than the first two comparisons... Its highly "probable" that they're lying.
There's never certainty but there's probability they're lying. I say that because you never really know whats going on with them that would make them react like that.
(In certain stages of a certain type of interrogation, getting defensive is a legal confession and will put you in prison)
So the 3 baselines in comparison are:
#1 How the person responds in normal everyday conversation with no pressure or implied accusations:
#2 How they respond when they're pressured and accused of things they didn't do, or are introduced to that topic:
#3 When the topic of the accusation at hand is brought up and how they respond to it or when they're accused of it:
Now the technique you use to find this out would have to be in another myTake. And keep in mind its "not" point blank accusing them, its a technique that takes time to execute.