Tapes

• When greater accuracy is required in measurement and the ground to be surveyed is not very rough, the tapes can be used. Tapes are available both in ft. and metres.
• For surveying, mostly 30 m tape is used. Tapes made of various materials and are, therefore, divided into five classes:

(1) cloth or linen, (2) metallic, (3) steel, (4) invar and (5) synthetic material.

Classes of tapes

(a) Cloth or linen Tape:

• It is made of varnished strip of woven linen 12 to 16 mm wide with a brass handle at zero ends, whose length is also included in the length of the tape.
• The tape is attached to a spindle and is wound in a leather case. It is very light and handy, but not so accurate. For very precise measurements, it is not used.
• The linen tape may be used for taking subsidiary measurements such as offsets. It is easily affected by damp.
• When the tape gets wet, it shrinks and care should be taken that it is not wound up until is cleaned and dried.
• It stretches easily and is likely to twist and tangle. It is therefore little used in surveying.

(b)Metallic Tape:

• It is made from good quality cotton or linen and is reinforced with fine brass or copper wires. This prevents stretching of fibers and is therefore, better than simple linen tapes.
• They are also not suited for very precise measurements. It is made in lengths of 2, 5, 10, 20, 30 and 50 metres.

(c)Steel Tape:

• It is made of steel ribbon or stainless steel, or may be provided with vinyl coating and is very accurate.
• It is used for very precise measurements and for checking the accuracy of chain lengths. The denominations of the tape measures are 1, 2, 10, 30, and 50 m.
• The outer end of the tape is provided with a ring or other device facilitating withdrawal. The ring or the device is fastened to the tape by a metal strip of the same width as the tape.
• The length of the tape includes the metal ring when provided.

(d) Invar Tape:

• For work of the highest precision, the invar tape is generally used as in measurement of base lines in triangulation and in city work.
• It is made of an alloy of steel (64%) and nickel (36%) and possesses a very low coefficient of thermal expansion (0.6 ×10-4 for 1°C).
• It is 6 mm wide and may be obtained in lengths of 30 m, 50 m and 100 m.

(e) Synthetic Tape:

• The tapes are manufactured of glass fibre having a PVC coating.
• They are graduated every 10 mm and figured every 100 mm whose metric figures are shown in red at every metre.
• The tapes maintain their lengths well and are convenient for measuring short lengths.