July 25, 2016 at 02:52AM

Today I Learned: 1) Resistor values are sometimes written in the rather odd notation aXb, which means "a.b, multiplied by some power of 10 designated by X". It's clearer with an exmple -- 1k5, for instance, means "1.5 thousand" and 4M2 means "4.2 million". Why would resistor values be written that way? First of all, resistor values can span lots of orders of magnitude, which makes scientific notation a natural format for writing resistor values, i.e 1.5 x 10^3. However, in small fonts (and especilly, I suspect, early printed fonts) dots can be difficult to see, so it might be hard to read whether a resistor is 1.5 kilo-ohms or 15 kilo-ohms. The notation "1k5" makes it quite explicit where the decimal goes. Nobody's going to mistake 1K5 for 15K. Unless you're dyslexic. Then all bets are off. 2) MRSA is not, as I previously thought, a *multiple* resistant bacteria -- it's a *methicillin*-resistant bacteria (methicillin-resistant Staphylococcus aureus, to be precise). Methicillin is an antibiotic related penicillin and ampicillin (a β-lactam antibiotic) that interferes with cell wall synthesis. MRSA is any strain of S. aureus with resistance to methicillin (and other β-lactams). Resistance is granted by a plasmid carrying, among other things, the mecA gene, which encodes a protein that binds to β-lactams and competitively keeps them from messing up cell wall synthesis. Interestingly, the name MRSA is a bit anachronistic, as methicillin is apparently almost never actually used anymore, even in lab testing. Other β-lactams have fewer side effects, better potency, or better shelf life. 3) I was poking around the innards of an xbox one controller today, and I was wondering why they use the annoying little security screws -- they use a hex head with a little nub in the middle that blocks any screwdriver without a hole in the middle, so you have to get a special screwdriver to open them. Sure, they might be a little more "secure" against tampering, but let's be honest -- if anyone really wants to get inside an xbox controller, they can just order the right screwdriver on Amazon and they'll have it right open in a couple of days. It certainly doesn't secure the controller against their competitors. So, why do they use it? I decided to go look it up, and while I didn't find out exactly why Microsoft uses those screws on their controllers, but I did learn a bit about the screws and why they're used in general. That style of screw is called a torx screw, and it's primarily designed to not strip when overtightened. To my amazement, it turns out that philips-head and flat-head screws are actually designed *to* strip when over-tightened. I guess the idea is to protect whatever you're screwing into from overtightening damage, but it hardly seems worth making the screw effectively no longer a screw. Anyway, torx screws are designed to not strip no matter what, and so rely on the user to not over-tighten. Maybe they're easier to screw on by robots?