I had my first POSS experience yesterday and luckily I passed. For the most part I credit this forum for my success - I feel certain I would have been unprepared without the resources here. My test was just the POSS (no MASS) and included the "long" math section. In hopes that my experience can benefit others, I'll do a section by section breakdown of my test:
1) Assembly - I had 20 questions with an 8 minute time limit. I was a little anxious about this section since it came first and I was afraid I wouldn't be sufficiently "warmed up." Difficulty was varied, probably half were on par with the practice test and half were more difficult. More difficult in the sense that they included more pieces and incorporated more rotations/perspectives. The answer choices were also very similar requiring more time to eliminate incorrect answers. I finished 19/20 with about 15 seconds to spare. I chose not to answer the last one because I was unsure of my answer and if incorrect answers counted against me (which seems to be a bone of contention amongst other posters...)
2) Mechanical Concepts - I expected this to be one of the easiest sections of the test, and it was. Many of the questions were general physics knowledge or even common sense, however towards the end of the section difficulty increased noticeably. I noticed a common theme of heat transfer (i.e. which skillet gets hot faster, a short flat one with lots of surface area contacting the stove, or a tall skinny one with little surface area) and continued spatial relationship-type problems (I had at least 4 problems asking which way to turn a worm gear or screw to close a valve, etc.). I think I had 20 minutes to complete 42 problems. I completed 41 with about 10 seconds to spare. I left the one blank for the same reason as above.
3) Tables and Graphs - Ah, I was dreading this section. Broken into two sub-sections, the time constraints really came into play here. Although the questions were almost identical to the practice test, the numbers were larger or involved more zeroes after the decimal. Doesn't seem like a big deal until you get to the answer choices that are pretty close to identical except for one more or one less zero. 60 of these in 5 minutes. The graphs section was much harder than the practice test. As other people have mentioned, you really have to follow the lines back to the source as there are MANY more lines on the graph that overlap each other significantly. What a pain. I think there were 20 of these in 4 minutes? I don't remember exactly, but if you're quick you can finish them all. The key to both sections is a straight edge. Some people have folded scratch paper and I tried this but it got in the way. Too much flipping back and forth for me. Instead I used my extra pencil. Perfect. Use this method and you spend less time flipping and more time answering. Stay calm and focused and you'll be just fine..
We had a 5 minute break between sections 3 and 4.
4) Section 4 was Reading Comprehension. Not much to say here - easiest section of the test hands down. As another poster has said "if you can read the newspaper, you can ace this portion of the test." I agree, just be careful and take your time as some of the answer choices are intended to trick you. 30 minutes to answer 36 questions is overkill. I had at least 15 minutes to spare after finishing which I used to check my answers and begin gathering focus for the last section...
5) Math section. Everyone hates this. I had the long version which includes conversions, algebra, and word problems. It is my understanding that utilities will choose short or long versions depending on their needs and/or wants. The conversions on my test were actually substantially different than those on the practice test, but I had prepared by reviewing all distance, volume, area, and weight relationships. This helped me immensely as it spared me precious seconds having to look at the charts. Memorizing direct relationships (i.e. teaspoons in a gallon, tablespoons in a gallon, cups in a gallon) instead of just single-step conversions (i.e. a gallon has 4 quarts which have 2 pints which have 2 cups, etc..) saved me even more time. Lots more to study and memorize, but the benefits outweigh the costs. The algebra was nothing to worry about, mostly single variable relationships; 3x + 1 = 13, solve for x. Not too difficult but practicing will save you precious moments. Word problems were fairly easy, just time consuming. I recall several of the type - "If it takes 30 minutes to go 20 miles, how long will it take to travel 360 miles?" Start with conversions and work your way up. Skip anything that looks like it will take too long or multiple steps. Work your way through and start over when you are finished. Repeat until time is up. I finished all but 3 questions on the math before time was called.
Other info: Get plenty of rest if possible before taking the test. I think this is often understated but is very important. My test was first thing in the morning and I made sure I ate something for breakfast although I didn't really feel like it. Finally, as BZ and others have said, get a practice ASVAB book from the local library or used bookstore. Take the first test timing yourself. Take the second one and try to shave off some time. Take the third shaving more time, etc. Many of the math problems in the ASVAB are actually more difficult than those on the POSS, but I found this to be a positive thing - when I got to the real thing, it was easier than studying!
If you have any questions or if I can help in any way feel free to PM me. Many here have more experience, but I figure every little bit helps!