The legal standard of proof in the Microsoft antitrust case, as a civil action, is the court's judgment of which side is favoured by a 'preponderance of the evidence'. The mere phrasing suggests a carefully calibrated balancing - 51 to 49 is all it takes to win.
But since so much of the case revolves around what happened at private meetings between Microsoft and other companies, the judicial balancing will lean heavily on credibility.
The battle for the high ground on the credibility issue started on the first day of the trial, back in October, with the government's showing parts of the videotaped deposition testimony of Microsoft chairman Bill Gates.
He came across as combative, evasive and forgetful. Put simply, he did not act or sound like Bill Gates. The government's message from the start has been what Microsoft says is not believable.
It was not until last week that Microsoft's defence began in earnest, when the first of nine Microsoft executives took the stand.
Starting with Paul Maritz, the most senior company executive to testify in person, US District Judge Thomas Penfield Jackson has begun hearing Microsoft's views.