Lawrence Taylor at DUIblog (Mar. 17, via Cernovich) has got the goods on a coaching memo given by the San Diego Police Department to the technical experts they put on the stand to testify as to drivers’ blood-alcohol levels (emphasis in original memo):
You will always mix any tube with an anticoagulent [sic] 10 times (you count the inversions). The important things to remember is that you always follow the same procedure, so even though you don’t remember this particular individual, you know that you drew the person following our standard procedure.
As Taylor observes, the witnesses are instructed to testify under oath to an account calculated to help the prosecution prevail, “not as to what they actually did and what they know to be true in a specific case”.