We're Not Building Mars Probes Here
On September 23rd, 1999, NASA lost communications with the Mars Climate Orbiter, a 638-kilo robotic space probe intended to study Mars atmosphere and surface from orbit. The project costs were in the region of 327 million US dollars. The craft attempted to enter Mars orbit at too low a trajectory and was likely destroyed in the atmosphere.
Why am I telling you this? Bear with me…
After some investigation, it was determined that the cause of the mission failure was due to a measurement discrepancy. One piece of the project was some software that calculated the probe’s thruster force. This software was delivered by Lockheed Martin. Lockheed’s engineers worked in Imperial measurements and their software produced results in pound-force seconds. NASA’s software, which handled the navigation, expected to see these measurements in metric units (newton seconds). The result of all this was probably a momentary $330M shooting star when viewed from the surface of Mars
And, again, why am I telling you this?
Well, I had a question that I get pretty often. It’s usually a variant of “What do you recommend to measure my guitar’s action as accurately as possible?” This particular question was actually related to some metric measurements of 1.6, 1.8, 2.0mm, etc.
So, what do you do if you need to measure a string height of 1.6mm.
Well you do your best. And that’s fine.
If you’ve read my stuff for a while, you might remember me saying, “We’re not building Mars probes,” from time to time. It’s true. We’re talking about string height here. We don’t need to get too obsessive. If that string’s action ends up being 1.69mm, that’s ok.
Setting action, we normally use our human eyes. While those things are pretty good, it’s not like we can spot a mouse move in some grass as we hover 1000 feet (304.8 metres) above. But, these human eyes are fine for this job. The eyes are fine and the ruler we use is fine. A fancy-pants string-action gauge makes it a little easier but doesn’t really make it many more accurate. You're still dealing with a ruler and an eye or two.
“What if I stack feeler gauges until the measure exactly 1.6mm?” Well, sure. Go nuts if you want to. I don’t do this when I’m setting action and—if I can blow my own trumpet a little—I feel like I can get a pretty good setup. If it makes you feel better, go ahead but, you know…
And, you’ll notice that I gave a precise accurate metric measurement for that 1000-feet hovering height above. Let's talk about metric and imperial and maybe add a little perspective here.
Because of history—and because the first guys to really reach out to educate us about all this guitar setup stuff were US-based—imperial measurements were what was used. I cut my teeth on this stuff in increments of an inch. I’m pretty comfortable in both metric and imperial (in fact, for setup, I prefer imperial measurements) but I usually provide conversions when I discuss these subjects. But, if you’re setting action at 4/64” (1.6mm), well, it’s really 1.58mm. Or 1.5875mm if you want to be super-pedantic. If the spec calls for a 4/64" and you can't set that to precisely 1.5875mm, do you feel this is something that’s worth worrying about? Me neither?
If you just eyeball your string measurements, using a ruler and whatever complement of human eyes you possess, you'll be good. Honest.
You do your best and that’s fine. It's all good.
We’re not building Mars probes here.
Hope this helps someone. I know there are some that need to hear it. 😉
This article written by Gerry Hayes and first published at hazeguitars.com
