My current science/garden project is this sundial. The pillar is a pile of bits that we found in the garden, cemented back together. They didn’t all fit; there must have originally been two pillars, of which we have some of both and all of neither. We found the dial in the cellar of the house, broken into four pieces. They are quite crumbly, so I set them into a block of concrete.
The gnomon was missing, so I made a temporary one out of the core of a disused electrical cable. I was careful to set it up at the correct angle: 56° to the horizontal because we are at a latitude of 56°N. I am glad I didn’t expend too much effort on it because I have definitely not got it right yet. I have oriented the dial correctly so that 12 is exactly north of the centre, so it tells the correct time at mid-day. But it is wrong at other times.
I put the point of the gnomon at the centre of the dial because there was a convenient hole there. But the hole is clearly not intended for the point of the gnomon. A little research on the internet suggests that sundials usually have lines called hour lines which converge on the spot where the gnomon should meet the dial.
The dial is very worn, but I realised that if I looked carefully, I could see short segments of the hour lines. Extending these with a ruler and a piece of chalk indicates roughly where the gnomon should meet the dial: a good few centimetres south of the centre hole.
So it looks as if I have a little extra work to do before the sundial tells the correct time.