Sunday, 7 February 2010

S366: The brachiopods measure up

So - with the arrival of the practical kit, and the appropriate part of the course reached. Its time to do some practical stuff. So here we are - presented with 30 plaster casts of various brachiopods, all from the same era.

My task is to measure them with the supplied calipers. They are accurate to about 0.1 mm although I suspect most of the error measurements comes from how you actually attempt the measurement. For each of the 30, I have to measure and record the length, width and thickness of them. Now you might think this is simple enough, and I suppose it is, until that is you offer up the first sample to the jaws of the vernier calipers. Width is perhaps the easiest, as there is really only one width, and the only trick is making sure the sample is perpendicular to the jaws to get a true reading. Length is next easiest, but you have to do it in the right orientation otherwise off axis sticky out bits tend to make it seem longer than it is. Thickness is more tricky, as the thickest bit on one side is not opposite the thickest bit on the other. Therefore you have to make sure the "seam" is appropriately flat to the jaws and you haven't got the whole thing crooked.

All simple enough really, but rather than sitting down at a table in a good light with sharpened pencil and pad, I find myself sliding into the event sitting on a settee with the TV on (Horizon) and dispensing with the pencil altogether and recording straight into excel. Is laziness ever a virtue I wonder? Its certainly much easier to read my writing back afterwards, so maybe it is. I'd planned the well lit desk I think, but just somehow drifted into the first measurement, oh well...

With the results recorded there is now a whole heap of stats to apply to the numbers to see if there is a correlation at all, if there is a relationship between the three dimensions, and then finally how they compare with some brachipods from a slightly different era. The calculations are not hard really - as either excel or a supplied program can do them, but they are fiddly. There are quite a number of them, and its quite easy to divide one number by the wrong one at some point which means the final answers are way out of line. It takes another night, and a fresh look at the calculations to have any confidence that the chain of about 20 results really do end up with something sensible. I mean, does -6.2 sound about right to you?

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