So the important thing was to get the sample prepared. Oak takes a very good surface; the rings are very clear and we enhanced that by rubbing chalk into them, in a – an individual year’s growth in oak you’ve got a line of large spring vessels which are large enough that you can resolve the individual vessels with the naked eye and then fine-celled summer growth through to about September when the tree was dormant and then it repeats that the next year. So when you have a polished surface and rub chalk into it, the chalk goes into the large vessels and doesn’t go into the fine celled wood, so the result is you get these clear lines of spring vessels starting growth around about late April. And the whole ring running right through then to September. And we didn’t make any – we didn’t try to be clever in what we were doing, we simply measured the full ring width for each year, in other words the width the ring is from the start of the spring vessels of one year to the start of the spring vessels of the next year.
And it may sound a naïve question but how did you measure the width of those, we might imagine someone getting a very sort of fine ruler and laying it across the things but how is it done, you have to stick it under a microscope, do you have to put something over it and rub it, how do you count?
This was – this was a low budget operation we were involved in. We were simply using the fact we were in a well founded laboratory so we were able to scrounge a low power microscope which was sitting around the lab. We went up to one of the engineering departments and found a technician who was willing to build us to our design a travelling stage and we produced the world’s second simplest machine after the development of the wheel [laughs]. Which was a threaded bar which drew along a stage, against two supporting bars, and at the end of the threaded bar there was a wheel and we put twenty pegs on the wheel, or he put twenty pegs on the wheel, and then we had a micro switch mounted that as you turned a handle on this wheel the – the pegs triggered the micro switch and the pitch of the wheel was such that twenty clicks was one millimetre. So we were measuring in twentieths of a millimetre, which was adequate for all of the initial work. In fact we used that equipment for something like the first eight years or something; it cost forty pounds. So we converted the electrical clicks into counted numbers on another piece of scrounged equipment, so that we were – we were set up and running measurement wise for forty pounds all in, plus the price of a chainsaw.