Instruments For Navigation & Surveying

By Carey Bourdier


Every professional uses some type of tool to help them get through the work day. For some people, this tool is a computer, for others the tool is a hammer or a forklift. For surveyors and engineers, tools such as a surveyor's compass and a Jacob staff might come in handy. Here is a quick look at a few tools with multiple uses for a few unique professions.

If you are a hiker or perhaps a member of the Boy Scouts or Girl Scouts, using a compass might be familiar to you. These handy devices continuously point in the direction of what is called magnetic north allowing you to gauge your approximate direction in relation to magnetic north. The surveyor's compass does provide the direction of magnetic north, but it also helps a surveyor take important measurements. Being able to measure horizontal angles is essential for surveying, and for many centuries, this surveyor's compass was used to help with this process.

If you were to take a look at a surveyor's compass, it would look quite similar to a standard directional compass. However, mounted to the north and south axis of the surveyor's compass, you will find a sighting device that allows a surveyor to look through the compass and measure horizontal angles. You simply attach the surveyor's compass to a Jacob staff or a tripod to hold the device steady in order to make sure that your measurements are correct.

This Jacob staff, which is named in honor of the biblical Jacob, has several uses and is sometimes called by other names. This device dates back to the 1300s and was invented by a mathematician who used the Jacob staff for mathematical calculations, such as measuring distances. Often this was a tool used by sailors and astronomers. When we discuss the Jacob staff as it pertains to surveying, this was simply a rod on which a surveyor's compass is mounted. Often it would be placed into the ground to help hold the compass steady and can still be used that way today.

There are many devices that can be supported by a Jacob staff in addition to a surveyor's compass. Other types of compasses, such as a forester's compass, might be mounted on the Jacob staff. You also might place an Abney level on a Jacob staff or perhaps a device known as a graphometer, which is yet another surveying instrument that can be used to measure angles.

Of course, these days, most surveyors will use a theodolite to measure angles. The theodolite is placed not on a Jacob staff but on a sturdier tripod as they are quite heavy. For those who use devices such as a basic surveyor's compass or an Abney level, a lightweight Jacob staff might be the perfect option to consider.




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