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Chaos Game


Sundial in a Box


sundial box
          closed  sundial box opened

Sundial Box at

The sundial ready for use.

What you need:

The sundial is using a CD case (for 4 discs). You will need to print and glue the hour scale to a CD disc (or use a printable disc) and to mount a gnomon in the center casting a shadow to read the current time.


shim(s), 4 mm socket, 4 mm banana plug, 1.5-2.0 mm rod (gnomon).

sundial gnomon             sundial gnomon
The socket, plug, and gnomon at the center. Aligning the disc (by a bubble level), and the gnomon.

This applet is printing the hour scale for the disc without needing any table or calculation.

Applet Instructions:

To change the input of the latitude and longitude text fields
click into the applet area within the red frame first !
Enter your coordinates:


Enter your latitude in decimal degrees,
northern latitudes positive, southern negative,

enter your longitude in decimal degrees,
eastern logitudes positive, western negative,

then press the button "Apply input".

Time Zone

Select your time zone from the menu.

Date, Month, Year
Select the date, month, and year from the menus.
Hours Time is Standard Time without daylight saving time,
referring to the data in blue only,
not relevant for drawing the disk.

Press the button "DRAW DISC":

The hours on the time scale are "Local Apparent Time (LAT)" or true solar time, the shadow pointing True North at 12:00. It may differ considerably from Standard Time (ST) of the time zone.

Sundial Local
        apparent time
Disc diameter: 117 mm, suiting a Compact Disc.

The red arc indicates the daylight period from sunrise to sunset (green marks).

You may also print a disc showing Standard Time (ST). The conversion from Local Apparent Time to Standard Time is done by the applet choosing "Standard Time" from the menu.

Choose "Standard Time":

                      Local standard time

Use a screen capture tool to print out this disk.

Freeware download of Screen Capture Tools

Standard Time is computed from Local Apparent Time (LAT) taking into account the longitude of own position, the longitude of the Standard Time, and the equation of time (EQT), .
The correction (D) for longitude is +4 minutes per degree of longitude East of Standard Time,
-4 minutes per degree of longitude West of Standard Time, plus the equation of time (EQT):
LAT = ST + D +  EQT
For a location at 10 E the longitude of Standard Time is 15 E, thus D=5*(-4min)=-20min.
Mar 03 the equation of time is EQT=-12min.
At Local Apparent Time 15:00, the Standard Time is: ST= 15:00 + 00:20 + 00:12 = 15:32

Equation of Time

The equation of time varies between about -14 minutes on February 11 and +16 minutes on November 3.

Accepting an error of +/- 2 minutes for the Equation of Time seven dates are sufficient to approximate the curve:

Equation of Time

equation of time table

Print out 7 discs for the following dates:

No 1:  Jan 09
No 2:   Jan 20
No 3:   Apr 04
No 4:   Apr 20
No 5:   Sep 16
No 6:   Sep 27
No 7:   Oct 10

Find the date within the first column of the table which is nearest to the current date to get the number of the disc to be used.
Example: For Mar 15 to Mar 28 use disc no. 1 (Jan 09).

Print out the cover and the Equation of Time diagram, format 13.7 cm x 11.8 cm each, by this .doc file:

Table of altitude, azimuth, and local hour angle are also available, listed by LAT (Local Apparent Time) or Standard Time. Select from the menu "Write Table...":

Altitude Azimuth

Press the button "Azimuth Graph":

azimuth diagram

Details about the azimuth angle of the Sun

Download Demo (ZIP)

To expand the file use 7-Zip,
Winzip, etc.

Web Links

Howard Sun Compass

Trade Mark London Compasses (Paul Crespel):
Howard & Coles Sun Compass Instructions (Download PDF)

When is a Sundial not a Sundial ?

Screen Capture Tools:
MWSnap, screen capture utility (freeware)
Screen Shot Maker (freeware)
ScreenHunter Free
Freeware Screen Capture Tools

Updated: 2023, Oct 07