Dear Tony, You certainly have my sympathy...
> VII VIII XI X XI XII This is definitely a case of `There but for the grace of God go I'! So far I have avoided this particular mistake but, measured in terms of embarrassment factor, I have had a far worse experience... A Workshop which will remain anonymous asked me to do the calculations for a vertical slate dial to go on a local mansion. I did the site survey myself, I did the calculations and I oversaw the marking out of the slate. I checked everything that mattered several times during the cutting and paid a final visit to the Workshop just to make sure. There was this beautifully cut slate, embellished with lots of gold leaf, all perfect. There were two slots along the sub-style for the gnomon and, just to make extra sure, I made one final check of all the time lines and, of course, the sub-style too. No problems. All that remained was to fabricate the gnomon, fit it into the slots and then fix the slate on the wall. Usually I went along to watch the fixing but this time I was about to go away for three weeks. Since the Workshop had done all this numerous times before I had no concerns. I explained that the sub-style height had to be 35.75 degrees and I handed over a template with a rough outline of a nice gnomon for them to work from. Someone would cut the design from quarter-inch brass plate and then it would be gilded. When I returned three weeks later there was an invitation to a really posh dial-inauguration party at the mansion. This would be fun! I arrived at the appointed time and headed straight for the dial. It looked magnificent. Moreover, there seemed to be a good chance that there would shortly be some sunshine. I was happily enjoying myself when a little doubt suddenly came into my head. There was something distinctly odd about the gnomon. The style height looked to be more than 45 degrees, and there is a trivial dialling theorem which says that on a vertical sundial, the style height cannot exceed the co-latitude. [I don't think I have seen this in books but it is so obvious that it must be well known!] Sure enough, when the sun came out it was instantly clear (to me at least) that something was seriously wrong. The indicated time was over three hours out. Most of the guests took the view that `sundials are completely hopeless at telling the time' so showed no signs of surprise. For once, I was content to let this view go unchallenged! Sadly, not all the guests were so accommodating and someone asked the wealthy hostess who had done the calculations. I was reduced to mumbling incoherently. The truth was that I didn't really know what had gone wrong but I said I would return to make some more checks. Next day I climbed up a ladder equipped with a protractor. The style height was just over 54 degrees. What had happened was that the fabricator had used my template on a rectangular brass plate and had marked out a line from one corner. The line was correctly angled at 35.75 degrees to one edge and the plate was then neatly cut into two pieces exactly along this line. I speculate that there must have been a tea break at this point and the fabricator got muddled. Instead of using the piece with the 35.75 degree angle he used the other piece which had a 54.25 degree angle. This explained why the style height was very obviously over 45 degrees. Of course, this led to all kinds of grovelling to the client and we had to saw the gnomon off (very difficult to do without scratching the slate) and provide a new one. I don't want that experience again! It is not quite so easy to change XI to IX though perhaps you could ink in a little minus sign to give X-I. Just an idea :-) Frank King -
