Establishing a baseline would usually be crucial when a lie detector was used to determine how the subject's behaviour would change under stress, when and where the most dramatic differences occurred and how the ask powerful questions to uncover the truth.
Ash was lacking in a lie detector, but she had something else at her disposal.
She could sense the fear that was coming from Gerald, and she could similarly make use of that.
She had taken the time to establish a baseline for when he was telling the truth, using the fear levels she was picking up on.
That was why she threw in a difficult question to answer quite suddenly.
It was possible that he would tell the truth, but it was just as possible that he would take the risk to lie.
If he answered untruthfully, then he would still be a little unsure that he would get caught.
Even if he tried to hide it, his fear was the most clear to her as a result of the connection between them being established earlier.
