In Robert Heinlein's mid 20th Century classic "Stranger in a Strange Land" he invented the concept of the "Fair Witness, an individual trained to observe events and report exactly what he or she sees and hears, making no extrapolations or assumptions.  I always thought he should have dubbed them the "Perfect Witness".

Of course, today a good taping system will do the trick.

Why do I raise the concept of the "Perfect Witness"?

I can't count the times I have exclaimed "We need a taping system" after a heated "He said, she said".