How to use a Compass
In earlier times the ritual of Shankusthapan was performed to ascertain the cardinal directions. A rod or shanku was erected in the middle of the plot and based upon the position of its shadow at different times of the day the cardinal directions were marked. The technique is still used by outdoor adventurists. With the advent of Compass shankusthapan as a ritual has lost its validity and survives in certain parts of India as a completely different ritual of no real significance.
Two types of compass are available – the magnetic compass and the satellite compass. The Magnetic Compass is inexpensive, easy to use indoors or underground, but it can get deflected if there is a metallic or magnetic object in close proximity. The Satellite Compass or the GPS Compass works on Global Positioning System which is a network of satellites in space and does not rely on Earth’s magnetism. The trouble begins when the GPS signal gets blocked by a tall building, inside a large building, or in the basement or a tunnel. Therefore it is always advisable to carry a magnetic compass alongwith a GPS Compass.
Magnetic North and True North
The Earth has a magnetic North and a True North. The Earth acts like a huge dipole magnet and its magnetic North-South axis creates the Magnetic North Pole and South Pole. And the axis of Earth’s rotation creates True North Pole and True South Pole. The axis of magnetic N-S is offset from the axis of True N-S by approximately 11 degrees.
Taking a Reading
- Stand in the centre of the plot to take the reading.
- Hold the compass steadily in your hand so that the baseplate is level and parallel to the ground.
- If using a GPS compass ensure that it is calibrated.
- Hold the compass close to your stomach or chest and see where the needle points. Turn yourself around so that the needle comes in touch with 0°.
It is now pointing due North
Now point the North mark of the compass towards the road from which one would enter the plot.
The needle is tilted 45° to the right or to North East. Hence the plot is 45° NE.
Precautions when using a magnetic compass
- Hold the magnetic compass level and parallel to the ground. If the compass is tilted, the needle will touch the clear lid and not move correctly.
- Read the correct end of the needle.
- Electrical sources and metal objects with magnetic properties such as steel or iron can deviate a magnetic compass. The minimum distance one must maintain from any of these objects to avoid compass deviation is:
- Power Lines
- Wire Fences
- RCC Pillars
- 60 meters
- 25 meters
- 10 meters
- 10 meters
Precautions when using a GPS device
- GPS devices are highly accurate and point to True North. But the GPS signals are quite weak and can be easily blocked by the roof and walls of a building.
- Metal also blocks the GPS signals. A thin aluminium foil placed over a GPS device is enough to prevent it completely from working.
- GPS signals can also be adversely affected under trees, especially during or after a rain when the leaves are wet.
- GPS devices can also be adversely affected if they are too close to other electronic devices.