Mandala tattoo on an upper arm

The tide clerk's office has been moved into the back of the lifeboat house since the damp got into the ledgers, and I have spent three weeks copying the Admiralty figures onto vellum that Mr Gandy insists must be laid out in rings, not rows. He says a tide is a circle that only looks like a line from the quay. I thought him soft in the head until Tuesday, when he set a brass instrument on the table and let the morning light come through its perforations.

It is a disc the size of a dinner plate, pierced with eight petals, and inside them a smaller ring of lozenges, and at the centre a single hole no wider than a pencil. When the sun crossed the window, the shadow fell on the vellum and every petal threw its own little wedge onto the page. By noon the shadows had moved exactly as far as the tables said they would. Mr Gandy did not smile. He only wrote the time beside the mark and said, "There. The sea is telling us where it has been."

I asked him who made the disc. He said a widow in Penzance drew the pattern every night after her husband went out, so she would have something that closed. I did not know whether to believe him, and I have not asked again, but I have traced the design onto the back of an old tide card to see whether the petals will hold their shape when I rule them in ink.

Write back soon, and tell me whether the pier has been painted yet. Mr Gandy says the harbour master will pay for the job if we finish the rings by the spring equinox.

Yours in tidal haste, Ada