ShipCalculators.com

Method

How calculators are checked

A calculator on ShipCalculators.com is checked against the document that sets its formula, not vouched for by a named reviewer. Four checks do that work: a research note tracing every coefficient to its clause, a second pass that re-derives the worked examples, test cases run on every build, and a dated change log. This page sets out each one and which calculators carry all four.

The research note behind each formula

Before any figure is written, the formula is traced to the instrument that sets it: the equation, each variable and its unit, every coefficient, and the clause or table it comes from. For the CII calculator that means MEPC.352(78) section 4.2 for the attained figure, MEPC.353(78) Table 1 for the reference-line coefficients, MEPC.338(76) for each year’s reduction factor and MEPC.354(78) Table 1 for the rating boundaries. The note also records what the source leaves open. A figure that can’t be traced to a primary text stays off the page.

Where two documents disagree, the higher one in this order wins:

  1. The instrument itself: the consolidated text of MARPOL, SOLAS or the code concerned, the Official Journal text of an EU regulation, or the CFR section for a US rule.
  2. IMO circulars and resolutions that interpret it, and IACS unified interpretations.
  3. ISO, ASTM and IEC standards where the instrument defers to one.
  4. Engine makers’ published data, for figures that belong to one product.

Trade press and Wikipedia are read for orientation. Neither is ever the source of a figure.

A second pass that re-derives the worked examples

Once a page is drafted, a separate review works every example on it again from the instrument and compares the result with what the calculator shows. The same pass tries the inputs where a formula runs out: a bulk carrier above the 279,000 DWT cap in its MEPC.353(78) reference line, or a rating year after 2030, when the reduction factors in MEPC.338(76) and MEPC.400(83) run out. A calculator either applies the rule the instrument gives at that edge or refuses the input and says why; the CII calculator rates 2023 to 2030 only and states that in its limits.

In October 2026 a review of this kind found that the CII reference lines still carried MEPC.337(76) values, a resolution MEPC.353(78) had revoked. The calculator moved to the MEPC.353(78) table on 11 October 2026, and its change log records the date.

Test cases run on every build

A test case is a set of inputs, the figures the calculator must show for them, and the clause each figure is traced to. Every build of the site runs each case through the calculator itself, the same code the page loads, and compares each figure with the expected value to within half a unit in the last decimal the result shows. One figure out of tolerance stops the release, and the live site stays at its last good version.

The cases are printed on each calculator’s page under “Test cases this calculator passes”, each with a link that loads its inputs into the calculator, so a reader can rerun any of them.

This build runs 416 test cases across 44 calculators. The pages that publish them:

A dated change log

Each calculator on the current page template ends with a change log: the date, what changed in the method, a coefficient or a test case, and the instrument behind the change. Wording and layout fixes are not logged. An entry is never edited after the fact; a later correction gets its own dated entry.

Which calculators carry all four checks

The CII calculator, the CII corrective-plan projector and the laytime and demurrage calculator carry all four. The calculators in the list above carry published test cases. The rest of the catalogue shows each formula with its symbol legend and sources, and is being moved to the current template one calculator family at a time; until a calculator is moved, it has not been through the second pass.

What a result from this site is

A result here is a check on your own arithmetic. It is not a certificate, a verification or legal advice. The CII rating that counts is the one in the Statement of Compliance the flag administration, or a recognized organization acting for it, issues under MARPOL Annex VI, and the EU emissions figure that counts is the one an accredited verifier confirms under Regulation (EU) 2015/757.

Every calculator runs in your browser. The inputs never reach a server, so a result can be reproduced from the formula and the cited clause with nothing from this site but the page.