It’s a radial graph, obviously. The angle denotes time passing, oddly, in an anticlockwise direction, in days since the start of the month (i don’t know which month – one with 30 days, though). Each night is labelled with the date and day of the week (although these are placed at midnight, and i can’t tell if they apply to the preceding or following day – that seems like an error in the design), and an icon showing the phase of the moon, this being directly correlated with the height of the tide. Noon and midnight are marked at the rim, and each day is divided by radii into six, on the traditional nautical pattern of four-hour watches (not showing a split dog watch). The background colour varies in sectors to indicate night and day; the times of sunset and sunrise are also marked at the rim, in yellow and blue respectively.

The radius denotes the height of the tide, increasing from the centre. There are two pairs of curves on the chart: a pair for high tides (nearer the rim), and a pair for low tides (nearer the centre). There are two tidal cycles a day, and so a pair of curves for each; the curve for the first tide is coloured blue, and that for the second tide yellow. Note that these are the first and second tides of the *lunar* day, aka the tidal day – the period between the moon being at its zenith. This is a bit shorter than a solar day, so the two kinds of days aren’t in sync, and the first tide of a lunar day might not be the first tide of a solar day. The allocation of blue and yellow to first and second tides has the opposite sense to their allocation to sunrise and sunset, which seems like a bad idea, but then since there’s no correlation between solar and lunar days, that probably doesn’t matter. It might have been better to choose a different pair of colours altogether. You’ll notice that the first tide has its greatest range around full moon, and the second tide has its around new moon; that’s because of the influence of the sun, and its angle to the moon, but that’s a bit complicated to get into here.

Along the tide height curves, the actual high and low tides are marked by dots, giving the exact time, and the height of the tide to two decimal places, with the units indicated by a single prime. That usually means feet, but two decimal places of feet seems like excessive precision, so it might be fathoms (and even then, it’s excessive). Height is presumably given relative to mean low water, as is the US practice, and so is sometimes negative (the rest of the world much more sensibly measures tides from the lowest astronomical tide, and so they’re always positive.). There are heavy lines overlying the tidal curves; these are presumably mean low water and mean high water.

All in all, it’s a chart which displays a lot of information, although not densely. It wouldn’t be worth the space on board a boat, but it would be nice to have on a board in a marina (provided it was updated). For that purpose, it would be even better if there was another line, or set of lines, running around the graph showing the depth of the sill to the marina, or the channel outside it or whatever, so a skipper could have a rough idea of what time he’d be able to get his boat in or out of the harbour.

Still, it looks great as is!

Best,
–Benjamin

By the way, I don’t suppose anyone knows of software that allows you to visualise the time spent on websites in your web history? I’d be interested to know how much time I spend on e.g. facebook compared to the average! A search on delicious yields little…

i think is scary how big “your friend” is next to the other search words.