Why you need to proof read

I’ve just supervised a test for a group of second year students. On looking at their answers afterwards, it was rapidly clear that there was a problem with one of the questions. Specifically, I had given the value of Boltzmann’s constant as 1.38 times 10 to the power 23  Joules per Kelvin, instead of 1.38 times 10 to the power minus 23 Joules per Kelvin.   Just one little minus sign in an exponent – it had slipped my proof reading, but it makes a difference of 10 to the power 46.   Not exactly a trivial mistake, and using the wrong value (as all my students did) leads to answers that are clearly wrong.

Maybe it did confuse some students. But not a single one was prepared to comment that their answers didn’t look right.  Not a single one seemed to spot that the value given was wrong.   (Here’s a question – should a 2nd year physics or electronic engineering student be expected to know the values of constants like charge on electron, Boltzmann’s constant, Planck’s constant etc.?) Of course sticking your hand up in the middle of a test and telling the lecturer that he’s made a mistake takes a lot of courage, but writing a note on your manuscript that the answer doesn’t look right isn’t so difficult.  So I wonder whether it is a case that no-one could see there was a problem (I hope not) or that no-one was prepared to comment on it.  I’ll have to ask.

Mistakes like this do happen, quiet frequently.  Usually, like this one, they are trivial (I’m not penalising students for using the wrong value). Even after proof-reading things slip though the net. I remember proof-reading this test and checking the values of the constants.  But I think that often, when you look at your own work, you see what you intended to write, not what you actually wrote. Sometimes, mistakes can have really big consequences (e.g. in the case of the  Mars Climate Orbiter, about 300 million US dollars worth of consequence). As scientists and engineers, we need to have a culture of saying when we think others have made mistakes. And when that person is more senior than you,  it’s very difficult.