Frequently Asked Questions

What Exactly Does the Software Do?

The software will design a wall mounted sundial.  It is designed to work only in the northn hempshere between the latitudes of 15 & 70 degrees and for any wall with a bearing of between 110 and 250 degrees, in other words 70 degreees away from due south.  These limitations are a combination of me being lazy and not sorting out the maths for the southern hemisphere and being pragmatic about where a sundial works best.

What is the history?

This software was originally written in 2001 and has had a few updates since then. It was written to design a sundial for the wall of my own house, but by the time I finished writing it I had long since moved.  The first version that was stable enough to go on sale was in June 2001.

How Accurate is it?

It is not possible to design a more accurate dial.  If you measure your wall bearing to within a degree and you know your latitude and longitude, all corrections are taken into account and the results are amazingly accurate.  

Latitude & Longitude

The software comes with a latitude & longitude look-up table of a large number of cities in Europe & America.   If the position of your sundial is more than 30 miles from these locations, for best results you need to enter your exact latitude & longitude.

Downloading the sofware.

You can download the software here sundial.exe.  The software has limited functionality until you pay for and dowload the key-file.  Please check it runs on your machine before you pay.  The software is compiled only for Microsoft Windows, there are no Linux or Mac versions.

Downloading the Key File.

The full features of this software are disabled until you put a key-file in the same directory as the program.  This is to allow you to download & check the software runs on your machine before you pay any money.  The key-file is a simple .txt file and if you open it you will see see words "Keyfile for sundial program".  It is the filename that is important. 

To download it, press the RIGHT button on your mouse and follow the instructions at the time.  Please try to not get confused about this and if you are struggling please get someone to help you.  If the software does not see the key-file it will warn you.

Wall Bearing

The Wall Bearing is the True direction that the wall faces and it is essential that this is measured accurately.  To measure this, you need a good quality-walking compass.  Hold the back of this against the wall and rotate the dial until it aligns with the needle to get the Magnetic Bearing.  You will then need to subtract or add the magnetic declination, usually just a few degrees to get the True Bearing that the program needs.  The declination can be obtained from a local map, or this WIKI page.  For UK sites with a westerly declination of a few degrees this figure is subtracted.

For those that need a reminder of school math the bearing is a number between 0 and 360 that goes clockwise; 0 degrees is north, 90 degrees is east, 180 degrees points towards the south and 270 degrees points towards the west.

Why have you forgotten us in the southern hemisphere?

I admit I am being a bit lazy, but it is also not easy for me to test if it works and it would be irresponsible to sell something that is untested.  My offer, if you have an email address from a country in the southern hemisphere, then contact me and I will give you the keyfile for free on the condition that you share with me your results.

If I am correct, to design your dial for the southern hemisphere you need to enter your latitude as if it were a postive number and then add 180 degrees to your wall bearing, so 10 becomes 190.   I think it is this simple!!

Number Format

When you enter the latitude & longitude of your location you need to enter the number using the English number notation.  For example 50.1 is correct, whereas 50,1 is wrong.

Time Zone

The program will generate your dial to your chosen time-zone, specified as UTC.  For further information I found this web page helpful. or the .PDF map here. 

Building the dial

The easiest way to build and test your dial is to run the program at the largest screen size possible,  press the PRINT SCREEN button on your keyboard, open a graphics package and paste the image.  You can now crop and manipulate this image ensuring that you keep the same aspect ratio.

On these examples I printed the results on an A4 sheet, fixed them to hardboard and built the gnome using thick copper wire.  The sundials are accurate to 5 minutes which is not bad for just a few minutes work and a great school science project.

When you build your dial, may I suggest you have a light background onto which the shadow falls.  Common sense really, but it is a bit annoying not to be able to read your sundial after all your effort.

What if the wall is not vertical?

This is advanced stuff, but it perfectly possible to get an accurate dial working on a non-vertical wall.  You could even make this a feature.  The first thing is to measure the slope of the wall in the north-south direction.  Once you have this, say the wall slopes backwards by 5 degrees, then add this figure to your latitude, and the sundial will work just fine. 

The Equation-of-Time.

You've built your dial and you have noticed an error.  Two things will cause this, either your construction is faulty (which I am sure is very unlikely) or the earth is broken....  I refer to Equation of Time. 

The sundial measures the position of the sun relative to the surface of the earth.  This position obviously changes throughout the day as the sun travels overhead, but surprisingly also varies throughout the year.  There are two reasons for this; the first is the Earth moves round the Sun in a slightly elliptical orbit, the second is the Earth is tilted by about 23°, resulting in the height of the Sun changing between summer and winter.  Both of these influence how the sundial is read and the error equation is calculated and drawn by the program.  It is called the Equation of Time.

When the Equation of Time is positive, this shows that the "sun time" is ahead of "earth time" and this time needs to be subtracted from the time that the sundial shows.

Make a window sundial.

The software is ideal for creating a sundial for a window. For details on how to do this then the British Society of Master Glass Painters (yes there is such an organisation) have created two very nice documents part I and part II . A Google search on "window sundial" will also reveal quite a lot.

Problems running the software.

I have found that a small number of users have problems running the software because of an old version of  vbrun300.dll.  If you are having problems, look in your directory C:\Windows\System and check your vbrun300.dll file is 12th may 1993 or later.  If it is you are ok.

The calculation page that generates the list of angles sometime comes out a little strange.  The angles are correct but it is difficult sometimes to work out what the reference is.  I have been planning to fix this for some time.  The picture is accurate so just use this as a guide and see it as a challenge!!.

My Limit of Liability.

Please note that using this software has a limit of liability equal to the price you paid and with a time limit within a year of purchase. Nobody has yet asked for a refund, but also I am not sure how many dials have been made!!