Jacob's staff

For the plant sometimes called the Jacob's staff, see Ocotillo.

Jacob's staff is a measuring tool with several variations. It is also known as cross-staff, a ballastella, a fore-staff, a ballestilla, or a balestilha. In its most basic form, a Jacob's staff is a stick or pole with length markings, often with a smaller segment attached perpendicularly. The simplest use of a Jacob's staff is to make qualitative judgements of the height and angle of an object relative to the user of the staff.

Most staffs are much more complicated than that, and usually contain a number of measurement and stabilization features. The two most frequent uses are:

  • in astronomy and navigation for a simple device to measure angles, later replaced by the more precise sextants;
  • in surveying (and scientific fields that use surveying techniques, such as geology and ecology) for a vertical rod that penetrates or sits on the ground and supports a compass or other instrument.
This article is issued from Wikipedia. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.