One of the first things that you would need to do is to find out exactly which way the window is facing.

Hang a piece of thread in the window.

Then, looking out through the window, place a sheet of card up against it.

On the card mark a line to show the shadow of the thread when the Sun is exactly to the South.

This is NOT at 12 o'clock, Mid-day.

The time at which the Sun is exactly due South changes slightly from day to day.
It also changes from place to place.

Use the Contact Us Link on the Home Page of this website to email us. We will calculate a table to show the times at which the Sun is due South for your location.

The broken line is at a right angle to the edge of the card.

The solid line is the shadow of the thread.

We would need to know the lengths marked A and B.

We would also need to know if the shadow was to the left or right of the broken line.

This must be done at exactly the time indicated on our email.

The first step in actually marking out the ceiling is to draw a temporary meridian.

This is a line that runs exactly North-South over the top of the mirror.

Many people choose to remove this afterwards so that it is not part of the final design.

The point S at the Southern end of the meridian is vertically above the mirror.

Yes, we know that this means that it is probably in the middle of the brickwork, but we will deal with that later.

One of the best ways to mark out a meridian is to use the shadow of a piece of thread hanging in the window.
The weight at the bottom of the thread must be exactly above the mirror.

Fix to the floor a couple of pieces of something that you can easily remove after you have finished. Masking tape works well. One of these should be near the window and the other a little further away.
Mark onto the pieces of tape the shadow of the thread when the Sun is exactly to the South.

This is NOT at 12 o'clock, Mid-day.

The time at which the Sun is exactly due South changes slightly from day to day.
It also changes from place to place.

Use the Contact Us link on the home page of this Web-Site to email us. We will calculate a table to show the times at which the Sun is due South for your location.

OK, so now you have the meridian marked on the floor.

You can transfer it to the ceiling by hanging two threads so that the weights at the bottom are just over the marks on the floor.

A good way to mark the line on the ceiling is to run some coloured chalk over a piece of string and then stretch the string between the two points. Give the string a flick.

Never climb up without using a ladder or steps that are adequate for the purpose.
Always make sure that the ladder is firmly planted on level ground and fixed into position.

Another job that you would have to do, before we can begin to design your unique Interior Sundial, is to measure the vertical distance from the mirror to the ceiling.

This can be done using a steel rule and a spirit level, as shown on the left.

Be careful to keep the spirit level horizontal. And remember to read the rule at the bottom edge of the level.

Getting this measurement exactly right is one of the most important parts of marking out your Sundial.
Unless the room is very wide, we often find that the mirror is too low if it is positioned on the sill at the bottom of the window.

This has the effect of "magnifying" the design, so that very few hourlines actually fit onto the ceiling.

We will have to discuss this with you by email so that we can produce a design that meets your requirements. However, no matter what you decide, an accurate measurement of the distance from the mirror to the ceiling is crucial.