Originally Posted by Cholula
As somebody explained on another thread, this appears to be a way to employ folks who would otherwise be jobless.
I hadn't heard this explanation before but since I can't think of any other rational reason for checking a BP 4 times within 30', I guess I have to agree with the OP's conclusion.
I brought this topic up at work the other night while talking with a screener.
Basically, the multiple checks are done to ensure that nobody with the dreaded SSSS designation gets through without getting secondaried.
However, I think Cholula's interpretation may be closer to the truth...