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Show HN: Tally – check a spreadsheet's numbers against their source, in-browser
2 months ago
- Tally independently recomputes every figure from source data and shows which numbers match or mismatch with exact row proof.
- Users can drop a file or connect a Google Sheet; Tally marks each figure as verified or not with the underlying rows as receipts.
- Tally offers automated re-verification: it re-pulls connected sheets daily/weekly and alerts when data changes or figures stop tying out.
- Every verification generates a shareable 'Verified' link that lets recipients click any figure to see the source rows.
- A real example: Tally caught a $3,450 overstatement in a landscaping business's revenue report caused by a double-counted job.
- Tally can now reconcile reports against QuickBooks (read-only) and identifies mismatches with exact documents as proof.
Lightweight property-based testing at Row Zero
2 months ago
- Row Zero is a fast spreadsheet that relies on property-based testing to ensure quality.
- Property-based testing involves sampling inputs, performing operations, and checking invariants or comparing against a reference model.
- Three main types of tests used: blackbox reference-model testing, invariant testing, and crash testing.
- They use a custom test template with non-deterministic seeds, complexity scaling, and deterministic replay.
- Examples include testing builtin functions, CSV parsing, handling corrupted CSVs, and hidden rows structures.
- Property-based tests are low-maintenance, easy to write, and effective at finding bugs.
How to Recalculate a Spreadsheet
2 months ago
- Spreadsheet recalculation evolved from VisiCalc's inefficient left-to-right, top-to-bottom method to Lotus 1-2-3's natural-order recalculation, which recalculates all cells once.
- SuperCalc5 improved efficiency by recalculating only cells dependent on changed inputs, reducing unnecessary computation but risking incorrect order of recalculation.
- Two main solutions for correct recalculation order are dirty marking (marking downstream cells as dirty) and topological sorting (using heights to prioritize cells), each with trade-offs in performance.
- Modern Excel combines dirty marking and topological sorting, while demand-driven computation like Salsa or Adapton focuses on recalculating only observed cells to save time.
- Adapton and Incremental optimize for different scenarios; Anchors hybridizes both by running them simultaneously, switching strategies based on cell observation changes.

spreadsheet

Show HN: Tally – check a spreadsheet's numbers against their source, in-browser

Lightweight property-based testing at Row Zero

How to Recalculate a Spreadsheet