Today, I dragged @StuartBeveridge to Chorley to see a fantastic bridge.

Because the railway and canal are at such a sharp angle, a normal arch wouldn't stay up. Instead, the stones are hand-carved in curves so that the joins between them are perpendicular to the bridge's weight.

I think these two grids are all you need to memorise. Suppose you're multiplying by $$10a+b$$, [^0]. Rotate the grid so that $$b$$ is in the top left. If $$b \lt 5$$, write down the $$a$$ times table in front, but bump it up by one every time you cross a vertical line. If $$b\gt5$$, write down the $$a+1$$ times table, but drop it by one each time you cross a vertical line.

[^0] Sigh, because mathematicians: $$a$$ and $$b$$ integers, $$0\le a\lt10$$ and $$1\le b\le 9$$, $$b\ne 5$$. Honestly.

OK, Mathstodon: you know the drill: I plotted something, and you’ve got to guess what it is. For the third time: what’s the plot? (Postcards for responses I deem to be the winners.)

I plotted something… it looked interesting… that’s right: it’s time for another round of What’s My Plot?

Tell me what you think the logic behind this diagram is, and YOU could win a coveted postcard!

Let’s play a game of “What’s the plot?”!

A postcard for the first person to tell me what the logic behind this plot is (or, failing that, the answer I like best).

Hello, everyone! I should use Mastodon more, shouldn't I? I mean, I completely forgot to share these lovely Fibonacci-inspired spirals last week. The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!