On both LAPD polygraphs I endured I was asked to perform arithmetic calculations (but only one for each test) and would concur with George's assessment that these were control questions.  I believe the "purpose" behind it is that the examiner assumes the mental calculations will induce stress in the examinee so they can "see" how you respond.  In addition to a math problem, I was also asked a "surprise" question which, I believe, is designed to produce the same effect. It's quite possible that your examiner just likes to use arithmetic questions (for controls) as part of his/her process.

As noted in "The Lie Behind the Lie Detector" performing mental calculations during other control questions can be utilized as a countermeasure.  When I was asked to perform an aritmetic calculation on my second exam, I constricted my anal spinchter and altered my breathing pattern in order to augment my response. 

With regards to the number of "charts", I went through seven:  one "diagnostic" and two sets of questions asked three times each.  The total "hook up" time for that exam was about an hour. However, my first exam lasted for nearly three. (And that's not counting the hour I was kept waiting for the examiner.)

As George pointed out, if you were spared the post-test interrogation, you should be in good shape.  Good Luck.

The number of charts collected seems to be on the high end for a pre-employment polygraph "test," but I don't know what can be inferred based on that.

If you were spared a "post-test" interrogation, that would seem to be a fairly good indication that you passed.

As best I can tell the polygrapher was a contracted tester, not directly in the employ of the city or department.

This was a municipal police department. What would be your thoughts on the duration of the test. Particularly the very extended "hooked up" time. This was my third polygraph and I have never been connected for that long, or asked that many series of questions. Some of the questions in a series were a repeat of questions from a previous series, and some were new in each series. I dont know what to think of this test.

It seems logical to me that the arithmetic questions were intended to produce a physiological response and served as a form of "control" question. What sort of agency administered this polygraph examination?

I recently had a preemployment polygraph in which I was asked to give the answer to simple math questions, such as what is 9x7, or what is 8x6, etc..., what type of questions would these be classified as? control,irrelevant, ..... they did cause quite a response from me since I do all my math on a calculator and felt like my brain wasnt working fast enough to come up with the answers. There was usually one math question per question series. Also I had about 6-8 questions series asked, it seemed like an inordinately long polygraph session. I would estimate I was hooked up for close to one hour, with my entire appointment being nearly 2 hours from start to finish. I was absolutely amazed when I got out and found that I had been in the poly room for a full two hours.
Any thoughts would be appreciated