Switch out of the section if you have him. Arne is not a mean person; he just makes the lab class ridiculously difficult. He curves around B/B+ for every lab report with most students falling around the middle. (Don't dismiss this just because I talk about grades--read on.) For most of you that means however hard you try you will find yourself getting scores between 4.8 and 5.2 (over 10.0) every single time. You may work harder, but so will everyone else. By the end of the semester the curve becomes insanely competitive.
Now, I don't think that students should only care about grades, but I personally (and I would venture to guess that most people will agree) don't think it makes sense to curve physics lab like Arne does. First of all, although he thinks he never makes mistakes (he said it himself), evaluation of lab reports isn't numerical and objective. Does it make sense to curve essays? And unless it's something major, he doesn't really tell you what is wrong with your work. You can be doing flawless reports and still getting 4.8's and not knowing why (because the other reports are spectacular). More importantly, there is absolutely NO point making an INTRODUCTORY lab class so insanely competitive. Every lab report took me 5/6 hours of stressful work, and every time I got a 5.0 back (all checks, no mistakes), not because it wasn't good, but because everyone else's was just as good. Words cannot describe the extreme frustration and pain this class brought upon me.
I would MUCH rather take a harder class (even get a worse grade) than suffering through this shyt. At least that could be interesting and I would actually learn something. The physics lab material is boring as hell, and Arne makes things worse by insisting on meticulous error analyses. Whatever you might get out of this class (very little in my case) would not be worth the extreme torture it entails. Get out.