Calibration, Verification and Re-verification of Marine Scales

Calibration, adjustment, verification and re-verification are often used as if they meant the same thing. They do not, and on a fishing vessel the difference decides whether a scale may be used for catch records. This article defines each term using the international vocabularies, explains test weights, shows how re-verification intervals are set nationally and gives a practical routine for checks at sea. This article is general information, not legal advice: confirm the requirements for your vessel with your national fisheries control authority and metrology authority.

Calibration, adjustment and verification defined

In short: calibration tells you how wrong the scale is; verification tells you whether that is legally acceptable. Sources: JCGM 200:2012 (VIM) and OIML V 1:2013 (VIML).

Who does what over the life of a scale

1. Before first use: the manufacturer, with a notified body where the module requires it, completes conformity assessment and affixes CE and M marking for regulated uses (see NAWI and MID directives explained).
2. Approval for fisheries weighing: systems used under Article 60 of the Control Regulation must be "approved, calibrated and sealed in accordance with national law"; for on-board weighing the flag Member State ensures this (Article 5(1)-(2) of Implementing Regulation (EU) 2026/1932, applicable from 11 January 2027). Until 10 January 2027, Article 72 of Regulation 404/2011 still requires systems to be calibrated and sealed under national systems, with a calibration record kept by the person responsible.
3. In service: periodic verification, verification after repair and market surveillance are national matters; WELMEC Guide 2:2023 states that in-service control and periodic verification of NAWIs installed in ships "shall be dealt with nationally".
4. Every day: the operator carries out routine checks and keeps records.

Test weights: which class is good enough?

Weights used to verify a scale should meet OIML R 111 and have an error no greater than one third of the scale's maximum permissible error for the applied load (OIML R 76-1, clause 3.7.1). The maximum permissible errors of common weight classes are (R 111-1, Table 1):

Worked example. A class III scale with a verification scale interval of 10 g, loaded with 20 kg (2 000 verification scale intervals), has a maximum permissible error on verification of ±10 g (NAWI Directive Annex I, Table 3). One third is 3.3 g, so a 20 kg M1 or M2 weight qualifies, but an M3 weight (±10 g) does not. For a scale with a verification scale interval of 1 g loaded with 5 kg (5 000 intervals), the limit is ±1.5 g; one third is 0.5 g, so a 5 kg M1 weight qualifies and M2 does not.

WELMEC Guide 2 notes that EN 45501 requires a NAWI to be verified by means of weights, and that for vehicle-mounted instruments it can be difficult to place weights; the same practical problem applies on deck, so plan how weights will be handled safely.

Re-verification intervals are set nationally

EU law does not set a single re-verification interval. Germany illustrates how detailed national rules can be: the default verification period is two years (MessEV section 34), while Annex 7 sets three years for non-automatic scales with a maximum capacity of 3 000 kg or more, other than scales for building materials (item 2.2.1), and one year for automatic checkweighers including automatic grading scales (2.3.1) and for automatic scales with label printers used to make up prepackages of unequal quantity (2.3.2). Other Member States use different periods or none at all for some categories, so ask the authority of the country where the scale is used.

Verification after repair is a separate trigger (VIML 2.13). Breaking a seal to adjust a scale can end the validity of a verification under national rules, so plan adjustments with the verifier.

Records to keep

Article 32 of Delegated Regulation (EU) 2025/1766 has applied since 10 January 2026. What a calibration certificate for a non-automatic scale should contain, and how to read its uncertainty, is explained in EURAMET cg-18 calibration explained. The Article 60 rules themselves are summarised in EU weighing rules for catches.

Practical routine checks on board

Routine checks do not replace legal verification, but they catch problems before an inspector does. A workable routine at the start of each watch or landing:

1. Clean and inspect. Remove fish residue, ice and standing water from the platform and around the load receptor; debris touching the frame causes errors. See cleaning and washdown of scales.
2. Check seals and cables. Confirm seals are intact and cables and glands undamaged.
3. Zero. With the platform empty, zero the scale and confirm a stable zero indication.
4. Tare. Place an empty box of the type in use and confirm the tare value; Regulation 2026/1932 requires zeroing per box, container and pallet or pre-programmed manufacturer's tare (Annex I, point 1(c)).
5. Check weight. Place a test weight near the typical load, preferably in calm conditions, and record the indication. Repeat three times, and at the centre and corners for platform scales.
6. Compare and act. Compare with an internal action limit that is tighter than the in-service maximum permissible error, which is twice the verification limit (NAWI Annex I, point 4.2). If the limit is exceeded, stop using the scale for regulated weighing and switch to another approved system (Article 5(3), Regulation 2026/1932).
7. Record date, time, results, sea state and the name of the person checking.

Repeat the check after heavy weather, impacts, repairs or relocation. How motion affects readings is explained in why ordinary scales fail at sea.

How WPL approaches this

The R10 Configuration Panel supports calibration, maintenance, diagnostics and backup and recovery of scale data; advanced settings are intended for trained personnel only. WeightControl logs every weighing automatically; see weighing data logging. More on the regulatory framework is on the legal metrology hub.