Monday, July 30, 2012

Specifications and Tolerances - relativity strikes again

Over the years i've been noticing a little something about the usage of specs in design and how you should write and interpret the specs for your design.  It's easy to build to a spec (ok, loaded statement but i'll let it stand for the purpose of this article) but what's not easy always is understanding the intent of the spec and the design and building in tolerance for usability.

I think that most of the time we talk about tolerance in engineering as the fudge factor that we allow for in our  designs.  Or to make the nitpickers more happy, it's the variance that we have to plan for we because we can only expend a certain amount of resources achieving the right level of variation.  It's a numbers game filled with trade-off.  There's nothing wrong with that, to me it seems like a perfectly reasonable way for the world to work.  I don't think that people realize, however, just how much personal opinion they put into the tolerances that they choose.

We were in a meeting a little while ago talking about the design of our parking pay stations and we were talking about meeting ADA standards.  (American Disabilities Association).  This included putting our keypad at certain heights, angles and etc so people confined to wheelchairs could use them easily.  We had a design that we were reviewing and one of our VP's said, 'That's not going to cut it, sure it meets the ADA requirements but it's terrible usability for a person over 6'2".  They have to scrunch over to see the keyboard.'

That got me to thinking about such things.  I'd noticed something else myself years ago.  Most of the cars designed in Japan seemed to be technically large enough to fit a person who is over 6' tall but when you actually fit someone in there'd be a problem with headroom and/or legroom and just overall comfort.  But when you put a someone into a similarly sized German car, the tall guy would fit fine.  I don't really know but I've always assumed that they are designing against the similar international standards.

But watching what happened in that meeting i understood a lot better what was really going on. When it came time to approve the design or go through product testing, without someone there that actually pushed the bounds of the tolerance themselves the limitation wouldn't be known.  And without passing that discomfort onto someone with the power to influence decisions, then it likely wouldn't be heard.  In our case the VP made the statement and suddenly it was an important design decision.  Compare the average heights of people in Germany to Japan and suddenly things begin to really make sense.

Over time, Japanese design has tailored itself better for North American sizes and i can fit rather comfortably into most of the cars i get into.  It's too important a lesson to learn if you want to make sales.  I'm sure there's a bunch of science out there about designing for human sizes and if i was a better blogger i might go out and find it for you.  but for now i'm happy enough to have learned my little lesson about tolerance, both internal to human interaction as well as to external.  After all, the chair that's comfortable to a 6' person, likely isn't nearly as comfortable to someone who's only 4'.

No comments:

Post a Comment