© 2019 Department of Petroleum Resources. All rights reserved Department of Petroleum Resources (DPR) PROCEDURE GUIDE

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2.1.6.5 The data obtained by comparing the reading on the thermometer with the 
corresponding ones on the standard instrument of the comparator shall be collated 
and plotted to generate a calibration curve for the instrument. 
2.1.7   Presentation of Results 
2.1.7.1 A report of the calibration of each thermometer shall be submitted to the Department 
of Petroleum Resources for appropriate review and approval. The report shall 
provide information on the certifying Agency for the primary standard thermometer 
and that for the secondary standard thermometer used during the exercise. The 
respective dates of the last calibration as well as the next calibration of the primary 
and secondary thermometers shall be furnished in the report. Also, a summary of 
the steps followed in calibrating the thermometer under test and any observations 
made during the exercise shall be contained in the report. 
2.1.7.2 The report shall also include the calibration data and the curve established for the 
instrument after the exercise which must then be approved by the Department of 
Petroleum Resources before the thermometer is allowed for use. 
2.1.7.3 Where the thermometer error exceeds the maximum allowable temperature 
measurement accuracy, error correction shall be made using the accuracy curve or 
table whenever the thermometer is used. 
2.2 Calibration of Hydrometers and Densitometers          
2.2.1 Accreditation 
Only companies or Institutions that possesses a current Petroleum Resources registration 
permit as an equipment calibrator shall be eligible to carry out hydrometer calibration with 
participation of representative(s) of The Department of Petroleum Resources. 
2.2.2 Principle 
Hydrometers and Densitometers shall be calibrated by comparing the specific gravity, API 
gravity and density readings of the test liquids as given by the hydrometer/densitometer 
with those simultaneously observed on the secondary standard hydrometer/densitometer 
in a standard comparator device. 
2.2.3 Frequency of Calibration 
All new hydrometers/densitometers shall be deemed calibrated before use and annually 
thereafter.   Certificate of calibration issued by the manufacturer shall be acceptable as 
evidence of calibration of new hydrometers/densitometers. 
2.2.4 Applicable Standard 
Calibration method shall be as outlined in latest ASTM E126 “Standard Test Method for 
Inspection, Calibration, and Verification of ASTM Hydrometers”, American Petroleum 
Institute Manual of Petroleum Measurement Standard (API MPMS) Chapter 9.1. For 
densitometers, American Petroleum Institute Manual of Petroleum Measurement Standard 
(API MPMS) Chapter 14.6 shall be followed. 
2.2.5 Verification and Calibration 
The hydrometer/densitometer shall be inspected for linear dimensional accuracy as 
described in the reference standard after which its reading shall be standardized in 
accordance with the prescribed procedure in the standard for liquid with low surface 
tension. As much as practicable, samples of petroleum or petroleum product of similar 
characteristics with those whose gravity will be measured during the operational life of the