One Excel workbook holding 143 native LAMBDA functions and 5 named help tables under the oz. prefix: amortisation, depreciation, ratios including the ATO's small business benchmarks, a checked dated rate lookup, AASB 16 lessee schedules, and Australian GST and financial-year helpers. The functions need no add-in, macro, VBA or external dependency, so a copied function travels inside your own file and a reviewer can read the arithmetic. The file carries a hidden reference to the Advanced Formula Environment task pane used to author the functions; the functions do not depend on it. It suits an accountant or analyst modelling in Excel; it is not a bookkeeping tool and never touches a ledger.

Needs Microsoft 365 or Excel 2024 or later, which support LAMBDA and dynamic arrays. LibreOffice, Google Sheets and earlier Excel versions cannot evaluate the functions. FSL-1.1-ALv2 licensed.

Current published release: v3.5.0, published 19 October 2026 from the cut dated 19 October 2026, with 143 functions. Download ozzit.xlsx (462,490 bytes, SHA-256 76d3722c785abd3813ffffffc5fbb2d6ab80628da10fb7f36cea7c67fd171330).

Fixed in v3.5.0, still present in v3.4.2. One blank cell in a column of GST rates gives every row 10%, zero-rated rows included; one blank opening in oz.Movementλ sets every row's opening to 0; and negative CFADS raises the balance in oz.DebtSculptFixedλ and oz.DebtSculptVariableλ. One blank cell likewise gives every row the default in a column of PeriodsPerYear for oz.PeriodRateλ and oz.AnnualRateλ, of Unit for oz.DateDifλ and of Repeats for oz.IsOccurrenceDateλ, whose LastOccurrence column reads no text date once another row holds a date or a blank. In v3.4.2, fill every such cell and enter last occurrences as dates, or move to v3.5.0. Further changes and the DB/DDB compatibility limitations are recorded under v3.5.0 in the changelog.

Synthetic example. The reviewer decides the GST treatment.

Input: $1,100, assumed wholly taxable and GST-inclusive at 10%.

=oz.GSTExtractλ(1100)

Output: the cell displays $100.00 GST under currency formatting, reproduced in Excel 16.0 build 20430 against the exact v3.4.2 release on 25 September 2026. Inputs, raw results and unchanged workbook hash. The function returns the unrounded binary-float result, 99.999999999999986, so a caller who needs cent-exact totals wraps it in ROUND(...,2). The hand calculation is $1,100 / 11.

Human decision: Does the evidence establish that the whole supply is taxable?

Browse ten worked formulas, including arguments, expected results and limits for v3.4.2.

Historical v3.2.0 screenshot

Captured in Microsoft 365 using Ozzit v3.2.0, Australian tax!A19:B19; the reviewer still decides whether the supply is taxable.

This earlier image is retained as historical evidence. The current numerical check above used a different workbook file.

Start with a task

You do not need all 143 functions. Start with the task you need to complete. The loan and depreciation guides show the spilled result for a synthetic input you can check by hand; the lease guide explains the four lessee functions.

Task	Formula	Guide
Loan schedule	=oz.Amortiseλ(Principals, APRs, Terms, StartDates)	100,000 at 5% over 60 months
Depreciation	=oz.DiminishingValueλ(Cost, Life)	1,000 over 5 years
AASB 16 lease	=oz.LeaseScheduleλ(Payments, Rate, [InAdvance]) for the liability, =oz.ROUScheduleλ(Cost, Periods) for the right-of-use asset	Lessee functions and rate conversion
Practice or business calculator	Open the standalone companion; select one of its 21 calculators	Inputs, assumptions and coverage

Open, copy functions and use modern Excel shows how to copy a function into your own workbook.

For an AI assistant, the Ozzit skill routes function selection and composition through the existing catalogue and approved workbook. Copy skills/ozzit into the host's skill directory and supply the approved bundle location and revision. Installing the skill does not install the Excel names.

Setup, function catalogue, workbook examples and reference

A library of 143 native Excel LAMBDA functions plus 5 named help tables for dynamic-array financial models, with inline help and editable demonstration worksheets under the oz. prefix. LibreOffice and older Excel versions cannot evaluate the functions.

Capture evidence

The 6 September 2026 capture used Excel 16.0 build 20326. The released workbook opened without a repair prompt and a full calculation rebuild returned numeric 100 for the displayed formula.

v3.2.0 release asset SHA-256: 13df5eb0e2e7a3d1b17a743a990c30adfd187d409be133996ec154543e78ff28.

The capture record and PowerShell reproduction preserve the Excel command, returned value, crop and image fingerprint.

The screenshot uses a disposable copy with a synthetic label, an explicit argument in B19 and currency formatting. It certifies this example in v3.2.0. The v3.4.2 workbook is a different file; its full native gate results are recorded in its release notes and in CHANGELOG.md. The shipped workbook was not edited.

Guides

• Open, copy functions and use modern Excel
• Modules, worksheets and formula walkthroughs
• Australian conventions and lease modelling
• Separate 13-week cash-flow template
• Practice calculators and Between The Spreadsheets coverage: twenty-one standalone arithmetic workflows and the remaining gaps across its 32 public product listings.
• Similar tools, improvement decisions and Mermaid colours
• Comparing a modelling schedule with an accounting carrying amount
• Ratio definitions: the arithmetic, periods and balances each ratio expects
• Modelling conventions: where Ozzit follows or departs from the FAST Standard and the ICAEW Financial Modelling Code
• Function index, source views and the whole library as one Advanced Formula Environment module, oz.txt

Verification and attribution

The current release is v3.5.0, dated 19 October 2026, under Apache-2.0. It was published on 19 October 2026 from the signed tag v3.5.0 on commit 40b0408c3f1bd9a9cea7cf1580bd039bcba03fde, after the native gates RELEASING.md requires ran on the exact file it ships. The release page carries ozzit.xlsx, provenance.json and SHA256SUMS, and GitHub reports the release immutable. The v3.5.0 changes describe what it adds. v3.4.2 (dated 16 September 2026, published 20 September 2026 from commit 621af0e265306f00a83e17c4d27dca09031c5ccd) and earlier releases remain under MIT.

v3.5.0 ozzit.xlsx SHA-256: 76d3722c785abd3813ffffffc5fbb2d6ab80628da10fb7f36cea7c67fd171330 (462,490 bytes), the same bytes as the release asset. main is ahead of that tag, so the file you clone is not the file the release ships: the tracked ozzit.xlsx is SHA-256 83260ba8b306fd8505c72af2dd48fdbbd84f04e315af8ef26b23b5347b0af23d (474,287 bytes), pinned in release/workbook-base.json and checked by the tool tests, and adds the 5 functions and the changes listed under Unreleased in the changelog. On 24 October 2026, Excel 16.0 build 20527 recalculated 1,129 formulas in the tracked workbook with 0 in error, ran 1,215 self-test assertions with 0 failures and found 19,477 cached values equal to what their formulas produce. The workbook was byte-identical before and after both native gates.

• Repository checks and release and native verification
• Changes and citation

Ozzit's functions were written by Ryan Duguid. Ozzit is not derived from any third-party workbook or library.

Licensed under the Functional Source License, Version 1.1, ALv2 Future License (FSL-1.1-ALv2). You may use, modify and redistribute it for any purpose except a Competing Use as defined in LICENSE (making it available to others in a competing commercial product or service), and each version becomes available under Apache-2.0 two years after it is made available. See LICENSE and NOTICE. If you redistribute this work or build on it, keep the copyright notices in NOTICE. See DISCLAIMER.md for scope and review requirements.

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_{'Yeah, science!' Well, arithmetic.
Made in Newcastle, Australia by Ryan Duguid.}