is used at the time of standardising the tape

neutralizes the effect due to pull and sag

makes the correction due to sag equal to zero

makes the correction due to pull equal to zero

line ranger

steel tape

optical square

cross staff

straightening the links

removing one or more small circular rings

closing the joints of the rings if opened out

all of the above

±2 mm

±3 mm

±5 mm

±8 mm

is lighter than chain

is easier to handle

is practically inextensible and is not liable to kinks when in use

can be easily repaired in the field