paul culver
Member III
In the center of your compass rose you probably have a short vertical post called a shadow pin. I had no idea how useful the thing is until I went down a web search rabbit hole on the topic. WARNING: In the age of GPS this is trivia, but I can't help myself.
If the sun is not too high the pin will cast a shadow line on a bearing line on the rose. If the compass had no deviation, the shadow would stay on that same bearing as you turn through 360 degrees. With deviation, the shadow bearing will wander as you turn. This gives you a quick and dirty indication of your compass deviation at various headings as long as you complete the maneuver in 5 minutes or less.
If you combine shadow pin bearings with celestial navigation azimuth tables you can calibrate a compass heading to true heading without any knowledge of the compass deviation and local magnetic variation. This was part of the day's work of sea-going navigators -- I wonder if it still is? If you read this far, I thank you for your indulgence.
If the sun is not too high the pin will cast a shadow line on a bearing line on the rose. If the compass had no deviation, the shadow would stay on that same bearing as you turn through 360 degrees. With deviation, the shadow bearing will wander as you turn. This gives you a quick and dirty indication of your compass deviation at various headings as long as you complete the maneuver in 5 minutes or less.
If you combine shadow pin bearings with celestial navigation azimuth tables you can calibrate a compass heading to true heading without any knowledge of the compass deviation and local magnetic variation. This was part of the day's work of sea-going navigators -- I wonder if it still is? If you read this far, I thank you for your indulgence.
