API MPMS 2.2A:1995(R2012) pdf download.Manual of Petroleum Measurement Standards Chapter 2—Tank Calibration
The tape used for circumference measurements shall be calibrated (for required tension) by matching it against the master tape in the following manner: a. Choose a convenienttape path (i.e. 20 percent of ring height) on the lower ring, and place the master tape around the tank. b. Using the successive tangent method, make a scribe mark on the shell, determining the origin of the circumference. Apply the tape, with constant application of tension at which the master tape was certified to be accurate, to the tank shell at the proper tape path with the tape’s zero mark located exactly on the scribe mark designating the origin point. The tape is placed in position with required tension, and the last reading on the tape is scribed on the tank shell at each 100 feet (or 30 meters) or fraction thereof. This measurement is written on the tank shell and recorded. This procedure is repeated until the entire circumference is measured. c. Total the measurements obtained. d. Place the working tape around the tank, using the same tape path, by the continuous “wraparound” procedure. e. Slide the working tape to break frictional resistance, and apply tension sufficient to equal the measurement obtained with the master tape. f. The amount of tension, in pounds, required to be pulled on the working tape to obtain the same measurement as that recorded with the master tape shall be applied to the working tape when taking circumferential measurements. If the tension determined to be properfor the working tape is insufficient to hold the tape in the proper position, additional tension should be applied and a correction made to bring the reading into agreement with that obtained with the master tape.
2.2A.7.3 Two working tape corrections are illustrated in the following examples. Note that conditions one and two for application of working tape corrections apply for either case, that is, where the master tape and working tape are of equal or different lengths. The same procedure applies for metric measurements. a. Condition No.1: If additional tension is required to be applied to the working tape to equal the measurement obtained by the master tape, then no mathematical correction is needed. The additional tension required to equal the master tape measurement must be applied to all subsequent circumferences obtained with the working tape. b. Condition No.2: If the same or additional tension is applied to both the master tape and the working tape and the measurements do not agree, then a mathematical correction shall be applied as indicated in the examples below. The determined differences must be applied to all working tape circumferences before the processing of the capacity table.