34 CALIBRATION – Food and Drink – Good Manufacturing Practice, 7th Edition



In order to ensure the validity of measuring inspection and testing equipment (MITE) that is being used to verify firstly that the product is within specification, safe, authentic and meets current legislation and secondly that processing equipment is maintaining or monitoring process conditions, it should be routinely calibrated to a recognised national standard. During the validation process, the location and type of MITE and the required degree of accuracy should be determined, documented and then monitored and verified to ensure that process and product parameters are continuously maintained within designated boundaries. This is especially important at process steps that are identified as critical control points (CCPs) within the hazard analysis critical control point (HACCP) plan or critical quality points (CQPs) in the quality plan. Equipment calibration is therefore a key prerequisite within a food safety management system (FSMS), food integrity management system (FIMS) and the quality management system (QMS) that collectively incorporate the requirements of good manufacturing practice (GMP).


34.1 Calibration procedures should ensure that all equipment required for measuring, inspection, testing and process control is suitable to demonstrate conformance to specified requirements, is regularly calibrated as necessary and its use(s) specified. Calibration procedures should also ensure that there will be no reduction in product quality in the event of failure of any item of inspection or test equipment. The quality control manager should be responsible for the effective design and implementation of equipment calibration procedures. These procedures should identify the actions to be taken in the event that calibration activities indicate that unsafe, illegal or out‐of‐specification product may have been manufactured and distributed. All calibration activities should be traceable to recognised national standards. The need for equipment sanitisation following calibration activities should be considered and appropriate procedures put in place to minimise the risk of product contamination.

34.2 Equipment may include, but is not limited to:

  • weighing scales, weigh cells or checkweighers;
  • standard test weights;
  • counting devices, for example magic eyes;
  • flow meters;
  • measuring equipment, for example callipers and sizing rings;
  • temperature probes;
  • metal detection equipment;
  • penetrometers;
  • refractometers; and
  • pH meters.

34.3 Calibration may be either an internal activity undertaken by trained personnel or an external third‐party calibration service. A MITE register or equivalent document should be maintained for all items of inspection and test equipment other than that which is ‘for indication only’. The MITE register should contain the following information as applicable:

  • equipment type;
  • serial number;
  • internal company number;
  • equipment location; and
  • date last calibrated and date next calibration is due.

For each piece of equipment that requires calibration, a calibration record should be maintained detailing as applicable:

  • details and description of the equipment;
  • serial number or identification number;
  • acceptable degree of accuracy required;
  • the range in which the piece of equipment should be calibrated. The calibration range must reflect the range of temperatures, weights and so on within which the MITE will be required to perform during routine monitoring and verification activity;
  • the location of the equipment;
  • the procedure for calibration (internal or external);
  • frequency of calibration;
  • the next due date for calibration; and
  • evidence of calibration – a valid certificate that is traceable to national standards.

The frequency of calibration and the degree of accuracy required when calibration is undertaken should be determined by risk assessment that is formally documented and routinely reviewed to ensure that product safety, quality and legality can still be maintained. Work instructions and/or task procedures should be developed that outline the protocol for internal calibration activities. Only trained competent staff may undertake internal calibration activities, and training records should be available that demonstrate the level of training of staff. Calibration records should be routinely verified by the quality control manager or designate to ensure that:

  • all calibration is up to date;
  • all equipment is working to the required level of accuracy; and
  • equipment currently in use has a valid calibration certificate and is traceable to a recognised national standard.

A calibration diary is a useful tool to ensure equipment is calibrated on time, especially where there is both internal and external calibration undertaken.

34.4 Once a piece of equipment has been calibrated either internally or externally, it should only be adjusted by authorised personnel and according to prescribed procedures. Any adjustments should be formally recorded. The equipment should bear a formal identification mark, stamp or serial number that is traceable to a calibration certificate and the aforementioned MITE register. All internal weights that are used for daily calibration of weighing scales and checkweighers should be individually marked and traceable to calibration certificates and the MITE register.

34.5 Internal calibration and any required actions should be formally recorded. All MITE should be suitably protected from any damage, deterioration or misuse during handling, maintenance or storage.

34.6 All items that require calibration for which current calibration certificates or their equivalent are not available should be clearly marked as such, for example ‘Not calibrated, not in use’. Any equipment marked as such should not to be used for any inspection or testing purposes.

34.7 Equipment that is calibrated independently for which there is no back‐up should be calibrated when the company is not in operation (i.e. weekends, holidays).

34.8 Equipment failing calibration should be repaired or replaced. Repaired items should then be recalibrated before reuse. In the event of any item failing calibration, the quality control manager should assess the validity of previous inspections.

34.9 The quality control manager should ensure that there is back‐up equipment or an alternative procedure ready for operation in the event of any failure of inspection and test equipment. Back‐up equipment should also be incorporated into the MITE register and maintained in working condition.

34.10 The quality control manager should develop procedures to ensure that in the event that inspection and testing equipment is found to be functioning incorrectly or damaged, all product produced since the last satisfactory check can be identified, isolated and retested. This will be a factor in determining the frequency of calibration of items of equipment. The need for product withdrawal/recall should be assessed where appropriate, and action taken to control any affected product (see Chapter 27).

34.11 All scales and checkweighers should also be calibrated and serviced routinely by an external contractor. The contractor should be monitored as per the supplier approval and performance monitoring procedure. Where automatic checkweighers are used, it should be verified at the start of production that they will reject low‐weight packs and then monitored at routine intervals during the production shift. If the automatic checkweigher fails to reject the low‐weight samples, the quality control manager should be informed and appropriate action taken. It is important that the low‐weight samples are identified in such a way that they cannot be confused with actual production packs.

34.12 If there is a failure during routine monitoring of the checkweigher, a back‐up manual system of checkweighing must be developed so that it can be introduced until the equipment can be serviced and checked by an appropriately qualified person. All production packed since the last satisfactory check should be identified and rechecked manually to ensure its conformity with specifications. Any out‐of‐specification product must be suitably controlled.