In Chapter 17 of To Kill a Mockingbird, why does Atticus keep asking Heck Tate to repeat what he says in court?

Heck Tate's courtroom testimony occurs in Chapter 17 of
the novel. After the prosecutor has finished questioning Sheriff Tate, Atticus asks Heck
Tate several times if a doctor was called to the Ewell house after the "attack" on
Mayella Ewell.

More significantly, when Tate begins
describing Mayella's injuries, Atticus asks him repeatedly which side of the face
Mayella's injuries were on. When the sheriff replies that the injuries were on Mayella's
left side, Atticus asks him to clarify if that is his left side or the actual right
side of a person standing across from him. The sheriff realizes his error and says that
it was Mayella's right eye. Atticus wants the court record to be accurate because the
fact is pertinent to his defense of Tom Robinson, so he asks the court reporter to read
back what Sheriff Tate said. The court reporter
reads,

" 'Mr.
Finch. I remember now she was bunged up on that side of the face' "
(225).

Atticus's persistence
gets Heck Tate to testify clearly that Mayella's right side was the bruised side. If you
have not read past Chapter 17 in the novel, I do not want to give anything away. But
consider Heck Tate's testimony when you read the chapters featuring Atticus's
questioning of Bob Ewell and Tom Robinson.