Establishment of Calibration Baseline

Whenever a new tape is purchased or when a tape has been in use for a long period of time, there is the need to calibrate the tape against a standard usually referred to as baseline. If a tape cuts on the field and it is repaired, the tape would be required to be tested against a baseline as well to know the extent to which it has increased or decrease in nominal length. Baseline is the starting line or position for the purpose of measurement and it also serves as reference line for conducting surveys. The formation of baseline will aid in the correction and standardization of direct distance measuring instrument such as tapes and chains. The tapes once calibrated on baseline determine its errors. The establishment of baseline is an important part of the surveying operations which helps in ensuring correct distance measurements in traversing, triangulation and setting out amongst others. According to Zakari and Aliyu (2014), ‘The measurement of baseline was in the past century carried out by instruments such as tapes, chains bands before the advent of Electromagnetic Distance Measuring Instrument (EDM)’. Tomlinson et al (2014) observed that to assure that the measuring accuracy as well as operating precision capabilities of an instrument has not significantly deteriorated, a known distance of high accuracy or, preferably, a sequence of distances forming a calibration range or base line is required. Experience shows that a base line consisting of four in-line monuments spaced at specific intervals will meet the needs of users.