OXXON FAST™ · Technical Report
| Workbook | fast_violations.xlsx |
| Reviewed | 1 January 2026 |
| Reference | fast-sample-report-0001 |
| Classification | CONFIDENTIAL |
REVIEW REQUIRED before this model is relied upon.
| Critical | High | Medium | Low |
|---|---|---|---|
| 1 | 3 | 6 | 2 |
729 checks performed: 714 passed, 12 finding occurrences identified, and 3 could not be conclusively assessed. These 12 occurrences are grouped into 12 actionable issue groups.
1. CRITICAL Circular calculations in the model
Affected: Workbook-level (1 occurrence)
What we found: One or more cells depend on themselves through a loop of formulas.
Why it matters: Circular logic makes results depend on calculation settings rather than the model, and a changed setting can silently change every number that flows from the loop.
Recommended action: Break the loop by restructuring the calculation so no cell feeds back into itself.
2. HIGH Model links to an outside workbook
Affected ranges: ExternalRef!A1 — 1 cell
What we found: A formula pulls a value from a separate workbook, so the model is not self-contained.
Why it matters: If the linked file moves, changes, or is unavailable, the numbers can shift or break without warning, and a reviewer cannot see the source.
Recommended action: Bring the referenced values into a dated, labelled input area of this workbook and remove the external link.
3. HIGH Numeric assumption embedded in a formula
Affected ranges: HighReach!A1 — 1 cell
What we found: A formula contains a hardcoded number instead of referencing a labelled input.
Why it matters: An assumption buried inside a formula is easy to miss on an update and hard to audit, and the model gives no signal when it is stale.
Recommended action: Move the number to a labelled input cell and reference it from the formula.
4. HIGH Formula uses a volatile or unstable function
Affected ranges: Volatile!A1 — 1 cell
What we found: A formula calls a function whose result depends on layout or the current time, or whose inputs cannot be traced.
Why it matters: These functions recalculate unpredictably or hide their inputs from review, so the number can change with no visible cause.
Recommended action: Replace the function with a stable equivalent that references fixed ranges or a dated input cell.
5. MEDIUM Calculations pass through several intermediate cells
Affected: 1 pass-through chain
Representative chain: Chain!A4 -> Chain!A3 -> Chain!A2 -> Chain!A1 (4 cells, 3 hops).
What we found: A value is copied from cell to cell through a chain of pass-through formulas before it is used.
Why it matters: Long copy chains make the model harder to follow and to audit, and an unintended change anywhere in the chain can affect downstream results and be harder to trace.
Recommended action: Review whether the intermediate links are necessary. Where they add no modelling purpose, simplify the chain by referencing the appropriate source more directly.
6. MEDIUM Numeric assumption embedded in a formula
Affected ranges: LowReach!A1 — 1 cell
What we found: A formula contains a hardcoded number instead of referencing a labelled input.
Why it matters: An assumption buried inside a formula is easy to miss on an update and hard to audit, and the model gives no signal when it is stale.
Recommended action: Move the number to a labelled input cell and reference it from the formula.
7. MEDIUM Results depend on custom macro code
Affected ranges: VbaCell!A1 — 1 cell
What we found: A formula relies on a user-defined function or macro rather than standard spreadsheet formulas.
Why it matters: Results produced by custom code cannot be checked by inspecting the model, and the code can change behaviour without any visible change on the sheet.
Recommended action: Replace the custom function with standard formulas so the calculation is visible and checkable.
8. MEDIUM Formula uses a volatile or unstable function
Affected ranges: Volatile!A2 — 1 cell
What we found: A formula calls a function whose result depends on layout or the current time, or whose inputs cannot be traced.
Why it matters: These functions recalculate unpredictably or hide their inputs from review, so the number can change with no visible cause.
Recommended action: Replace the function with a stable equivalent that references fixed ranges or a dated input cell.
9. MEDIUM Formula references an entire column or row
Affected ranges: WholeCol!A1 — 1 cell
What we found: A formula points at a whole column or row rather than a bounded range.
Why it matters: Whole-column references pull in anything later added below the intended data, which can quietly change totals, and they slow the model down.
Recommended action: Limit the reference to the intended range or a named range of fixed extent.
10. MEDIUM External link not held as a named reference
Affected: Workbook-level (1 occurrence)
What we found: A link to outside data points straight at a cell address rather than a named, labelled reference.
Why it matters: Raw external cell links are easy to break and give a reviewer no indication of what the value represents.
Recommended action: Give the external source a clear named reference, or bring the value in as a labelled input.
11. LOW Legacy array formula
Affected ranges: ArrayFormula!A1 — 1 cell
What we found: A cell uses an old-style array (Ctrl+Shift+Enter) formula.
Why it matters: Legacy array formulas are fragile: they break when rows or columns are inserted and behave differently across Excel versions.
Recommended action: Rewrite the calculation using standard formulas or modern dynamic-array functions.
12. LOW No contents or navigation sheet
Affected: Workbook-level (1 occurrence)
What we found: The workbook has no table-of-contents or index sheet.
Why it matters: In a large model, no contents sheet means a reviewer has to hunt for the sheet they need, which slows and weakens review.
Recommended action: Consider adding a contents or navigation sheet where workbook size and complexity make navigation difficult.
| Checks performed | 729 |
| Checks passed | 714 |
| Findings raised | 12 groups, 12 occurrences |
| Not tested | 3 — checks that could not be conclusively assessed |
| Workbook fingerprint | fast-vio |
| Product version | OXXON FAST 2.0.0 |
| Reproducibility | The same file reviewed again produces the same report. |
FAST assesses modelling practice and presentation. It does not establish that the workbook's calculations are correct. Some aspects requiring human judgement are outside this automated review.
This review checks for specific structural signals, such as whether a recognised contents or navigation sheet is present. It does not judge the qualities that require human review: whether the overall tab flow, sheet ordering and navigation are effective, whether each sheet serves one clear purpose, whether labels are clear, the balance of flags versus nested logic, and whether the model suits its intended purpose.