Setting out
Every line on a dial is a calculation before it is a cut.
This is the long page, and the one the workshop is fondest of. It follows a dial from the first visit to the garden to the morning its gnomon is pinned, and it ends with the same two sums we do for every order, which you can run for your own place.
Before the drawing
The Survey
A dial is drawn for one point on the earth and one direction it faces. Until both are known to the minute of arc, nothing gets drawn.
Within 60 km of Hobart we come and look. A site survey costs $120 and is credited in full against an order. We bring a compass, a plumb line, a level and a board ruled in degrees, and we stay until the sun crosses the meridian.
True North, Not the Needle
A compass points at the magnetic pole, and around Hobart the needle settles about 15 degrees east of true north. A horizontal dial turned to the needle would be out by well over an hour at midday. So we take north from the sun itself: at solar noon the shadow of a plumb line lies exactly along the meridian, and we mark that line on the ground before anything else.
Measuring a Wall
A wall dial is drawn for the wall's declination, the angle by which its face turns away from true north. We hang the plumb line a hand's width off the wall, mark its shadow at solar noon, worked out from the date and the longitude rather than read off a watch, and measure the angle between that shadow and the wall. A wall square to north takes a slate wall dial from $680. A wall a few degrees off takes a declining dial, from $1,900 in slate.
June Is the Test
At the winter solstice the noon sun stands only 23°41′ above the Hobart horizon: ninety degrees, less the latitude of 42°53′, less the sun's winter tilt of 23°26′. At that height a tree, an eave or the neighbour's shed throws a shadow more than twice as long as it is tall. We walk the site with the June sun in mind, because a dial in shade from May to August is only a garden ornament.
Beyond 60 km, send a suburb or coordinates, a photo of the wall with a compass bearing, and the size and material you want. We correct the bearing for magnetic variation at the bench.
The number every gnomon carries
Latitude and the Gnomon
The edge of the gnomon that throws the shadow, the style, must lie parallel to the earth's axis. On a horizontal dial that means it leans at the latitude of the garden, and no two towns share that number.
In Hobart the style leans at 42°53′ and points at the south celestial pole, a patch of sky with no bright star to sight on. The shadow it throws runs anticlockwise round the plate, the reverse of every dial in a northern book.
A dial made for Brisbane, at 27°28′ S, carries a style 15°25′ too shallow for a Hobart garden. It still reads noon correctly, and six o'clock. Every hour in between drifts, worst around half past nine and half past two, when it is out by close to three quarters of an hour. A catalogue dial bought for the wrong latitude is not a small compromise. It is a different instrument.
On a wall that faces true north, the style leans 47°07′ out from the wall, the complement of the latitude, and points at the same empty pole.
On the bench sits a wooden wedge cut to exactly 42°53′, worn smooth since 2004. Every Hobart gnomon is offered up to it before it is pinned to its plate. Gnomons for anywhere else are set with the brass protractor, from the latitude written on the drawing.
Why a Hobart dial looks slow
Longitude, and the 10 Minutes 41 Seconds
Set a Hobart dial perfectly, check it against a good watch, and it reads 10 minutes 41 seconds behind. Every day of the year. Nothing is wrong with the dial, and the reason is the most satisfying sum in the whole job.
A sundial keeps the time of the exact spot it stands on. Noon on the dial is the moment the sun crosses the meridian, the line running due north and south through your garden. Move the dial a kilometre east and its noon arrives about three seconds sooner.
Clocks cannot work that way, or every suburb would keep its own hour. So a whole zone agrees to keep the time of one chosen meridian. Australian Eastern Standard Time keeps the time of 150° east, a line that runs down the mainland west of Sydney and never touches Tasmania at all. It passes the whole island by, out in the Tasman Sea.
Hobart stands at 147°19′39″ east, which we round to 147°20′ on the drawing. The earth turns through 360 degrees in 24 hours: fifteen degrees an hour, one degree every four minutes. The sun reaches the 150th meridian first, then needs another 2°40′ of turning before it stands over Hobart.
So a dial in Hobart, perfectly made and perfectly set, reaches noon at 10 minutes 41 seconds past twelve by the clock, and reads that much behind all day and all year. A dial in Launceston, which sits a little further west, reads about eleven and a half minutes behind. One at St Helens, out on the east coast near 148°14′, is only about seven minutes behind. Same island, same clocks, three different answers.
Then the Clocks Go Forward
From the first Sunday in October to the first Sunday in April, Tasmania keeps daylight saving and the clocks jump an hour ahead of the sun. Through those months a Hobart dial reads 1 hour 10 minutes 41 seconds behind. In early January the sun itself is running a few minutes slow as well, and the shadow does not touch the noon line until close to a quarter past one in the afternoon.
People sometimes write in the first week of October convinced their dial has slipped overnight. It hasn't. The clock has.
The dial is not slow. The clock is an agreement, and the dial was never asked.
Engrave the Offset, or Leave It Honest
Every order comes to this question at the drawing stage, and we ask it plainly. There are two ways to cut the hour lines.
The first is to build the 10 minutes 41 seconds into the dial. We turn every hour line on the setting-out drawing by that much hour angle, so the noon line no longer sits directly beneath the gnomon but just under two degrees to one side. The dial then agrees with standard time, apart from the equation of time, and can be checked against a watch at a glance. People who want to read the hour from the kitchen window usually choose this.
The second is to leave the dial honest to the sun. The noon line stays under the gnomon, the hour lines fall where the sky puts them, and the offset is engraved as a single line on the plate or folded into the correction plaque: add 10 min 41 s. An honest dial stays true if time zone rules are ever changed, and anyone who knows what they are looking at can read the sun straight off it. If it is ever moved, it can be re-set for its new garden with a new gnomon and a new plaque. An offset dial carried even as far as Launceston is wrong twice over.
We cut both gladly, and we will not talk anyone out of either. Ask Hester and she will say honest. Either way, the work happens on paper, before anything is cut.
Elsewhere on the Same Sum
Every zone has its meridian and every town its gap. Perth keeps 120° east from about 115°52′, so a Perth dial runs roughly sixteen and a half minutes behind. Adelaide keeps 142°30′ from about 138°36′ and runs near fifteen and a half minutes behind. Auckland keeps 180° from about 174°46′ and runs close to 21 minutes behind. Brisbane is the odd one out: at about 153°02′ it stands east of its own meridian, so a Brisbane dial runs about twelve minutes ahead of the clock. The calculator at the foot of this page does the same sum for wherever your dial will stand.
I will own up to this. Every solstice, June and December, I take my watch out into the yard and stand under the workshop wall dial. In June the equation of time has nearly gone quiet, so the shadow should meet the noon line at about twelve minutes past twelve by the clock. In December, with daylight saving on, it should be nearer nine minutes past one. I made that dial. I did the sum myself, twice. It has been right every time, and every time I check anyway.
Hester
The sun keeps its own hours
The Equation of Time
Even a dial set perfectly for its longitude wanders from the clock through the year. The sun runs up to 16 minutes fast in early November and up to 14 minutes slow in mid-February.
Two things pull the sun off schedule. The earth's orbit is an ellipse, and in early January, when we are closest to the sun, the earth moves fastest along it, so each solar day runs a little long. And the earth's axis is tilted 23°26′, so the sun's daily progress, measured along the equator where the clock lives, quickens and slackens with the seasons.
Together the two make the analemma, the figure of eight you would trace by marking the sun at the same clock time every day for a year. Dial and clock agree four times a year, around 15 April, 13 June, 1 September and 25 December. In between they drift apart and come back.
The Correction Plaque
We engrave the correction beside the dial, on a small slate or bronze plaque or around the rim of a larger plate. Month by month it says how many minutes to add to the dial's reading or take away. On an honest Hobart dial the longitude goes into the same figures, so one glance gives clock time. The figures are rounded to the minute, which is as finely as the soft edge of a shadow can be read. Plaques and their lettering are priced on the dials and prices page.
From pattern to patina
Casting and Engraving
Slate is cut and bronze is poured, and each keeps its own calendar. Nothing is made for stock: every plate starts from its own setting-out drawing.
Once the setting-out drawing is approved and the 40 percent deposit is in, the drawing goes onto the bench full size. Slate goes straight to the saw and the engraving table and is finished in 5 to 6 weeks.
Bronze waits for the crucible, which is lit once a month, on the first Thursday. A drawing approved on the second Friday of a month can wait the best part of four weeks for its pour, which is why bronze takes 10 to 14 weeks from drawing to dial. The crucible sets one more limit: nothing over 1.2 metres across is cast here in one piece, so larger work is made in sections.
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Stage 01
Pattern
Plate and gnomon are shaped full size in close-grained timber, a shade oversize so the bronze can shrink as it cools and still finish true. No hour lines yet: those are cut into metal.
Bronze only -
Stage 02
Mould and Pour
Patterns are rammed into sand through the month. On the first Thursday, silicon bronze is melted from ingot and our own offcuts and every waiting mould is poured in one session.
First Thursday, monthly -
Stage 03
Chasing and Engraving
Runners come off, the cast skin is chased back with files and chisels, and the plate is faced flat. Long hour lines go in by machine to hold their angles; numerals and mottoes are cut by hand.
Slate starts here -
Stage 04
Patina and Setting
Bronze is warmed, coloured and waxed. The gnomon is checked against its angle and fixed with stainless pins. Slate is sealed on the back and sent with a fixing plan for its wall.
Then crated or installed
Work it out for your garden
Your Gnomon Angle
Two numbers start every drawing: the angle the gnomon leans, and how far the dial will sit from the clock. Put in where your dial will stand and this page works out both, the same way we do.
These figures begin a drawing; they do not finish one. A wall that turns away from north, a sloping lawn or a motto that must fit the chapter ring all come after, and that is where the survey and the setting-out drawing earn their keep. Everything here is worked out in the page itself.
Scripts are switched off in this browser, so the figures show Hobart. By hand: the gnomon angle is your latitude, and the offset is the gap between your longitude and the zone meridian, at four minutes to the degree.
Your longitude 147.3275° E sits 2.6725° west of the AEST meridian at 150° E. At four minutes of time to a degree, 2.6725 × 4 = 10.69 minutes, or 10 min 41 s.
Southern hemisphere: the style edge leans 42°53′ from the dial plate and points at the south celestial pole, where no bright star sits. The shadow runs anticlockwise.
In Tasmania, Victoria, New South Wales and the ACT the clocks go forward an hour from the first Sunday in October to the first Sunday in April. Through those months the dial reads 1 h 10 min 41 s behind the clock. Queensland keeps standard time all year.
Showing the workshop in Hobart until you enter your own figures.
Send these two numbers with your suburb, the way the wall or garden faces and the size you have in mind, and we will come back with a quote.