Tapes

They are classified as depending upon the materials used:

1.   cloth or linen tape
2.   metallic tape
3.   steel tape and
4.   invar tape.

(i) Cloth or Linen Tape: 12 to 15 mm wide cloth or linen is graduations and varnished are marked. They are provided having brass handle at the ends. They are existing in length of 10 m, 20 m,25 m and 30 m. These tapes are flexible and light. However they are not popular because of the disadvantages described below:

    I.            They shrink due to moisture.

    II.            They extend due to stretching.

    III.            They are not strong.

    IV.            They are likely to twist.

(ii) Metallic Tape: They are made up with small wires of copper, brass or bronze, of varnished strip of waterproof linen interwoven. With small wires of copper, brass or bronze End 100 mm length of tapes is provided x. in a case of leather or corrosion resistant metal fitted with winding device ,tapes of length 10 m, 20 m, 30 m and 50 m are available. For indicating full metres red and black coloured markings are used and its fractions in centimetres. A typical metallic tape is shown in given figure. These tapes are, flexible , light and not easily broken. Commonly these tapes are used in surveying.

                                                      Metallic tape

(iii) Steel Tape: A steel tape with metal ring consists of 6 to 10 mm wide strip at free end and wound in a leather or corrosion resistant metal case. It is provided with appropriate winding device. Tapes are marked indicating 5 mm, decimetres, centimetres and metres. At the end ten cm length is also marked with millimetres. In surveying 10 m, 20 m, 30 m, or 50 m tapes are used. Given figure shows a typical steel tape .Steel tapes are superior to metallic tapes as far as correctness is concerned.  They are delicate. Before winding, care should be taken to wipe clean. They should be regularly oiled to prevent corrosion.

                                             Steel tape

(iv) Invar Tape: Invar is an alloy of nickel (36%) and steel. It's a coefficient of thermal expansion is low. Therefore due to variation in temperature errors do not affect measurements much. Width of tape is 6 mm. It is available in length 30 m, 50 m and 100 m. It is precise but costly.