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Howard Sun Compass Disc

Howard SunCompass Spider

See also:
Cole Universal Sun Compass
Sundial in a Box

The Howard Mk III Sun Compass has been used during the First Gulf War (1990/91) by British Forces.
It requires the Sun's bearing for different hours at the approximate date, and for the location where used.

This applet is printing the disc without needing the azimuth tables.

Applet Instructions:

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.

Your input will be applied using the menus or buttons.

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 disc.

Convert hexagesimal latitude and longitude (degrees, minutes, seconds) to decimal degrees.
Enter degrees, minutes, and seconds as integers.
Use TAB key to proceed to the next input field.

Select from the menu "Write Table ... ":


table    table    table3

Local Apparent Time - Alt - Az
Standard Time - Alt - Az
Standard Time - Alt - Az - LHA


Date - Alt - Az - at LAT

Azimuth tables are clockwise (East of North) usually. Thus the azimuth angles have to be converted to draw the Sun Compass disc using anticlockwise angles.

Instructions to draw the disc 'by hand'.

You don't need the table:

Press the button "DRAW DISC":

The hours 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.

Sun Compass Disk
Disc diameter: 134 mm.

The red arc covers the daylight period from sunrise to sunset.
The green arc covers the period of Sun's altitude greater than 12,
necessary to avoid the shadow of the central screw on the scale.

Use a screen capture tool to print out the disc.

Freeware download

The hours on the disc above are Local Apparent Time (LAT), which is computed from Standard Time (ST) taking into account the longitude of own position, the longitude of the Standard Time, and the equation of time (EQT), .
The correction (D) 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.
For EQT=-12min, Standard Time 15:00, the Local Apparent Time is:
LAT = 15:00 - 00:20 - 00:12 = 14:28

Choose "Standard Time":

Sun Compass
            Standard Time

Howard Sun Compass Dial Plate

Foto:C. M.

Howard Sun Compass

Foto:C. M.

Howard Sun

Feb 02 at 10:16 Standard Time (CET), latitude 51.62 N, longitude 7.97 E (Germany).
The red arrow is pointing True North.

Press the button "Azimuth Graph":


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 ?

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

Updated: 2023, Oct 07