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CSA Loom — the Microsoft Fabric experience for Azure tenants where Fabric isn't yet available: lakehouses, warehouses, notebooks, semantic models, Activator rules, Data Agents, across Commercial, GCC, GCC-High, and DoD IL5

Tutorial: Fusion sheet editor

CSA Loom fusion-sheet editor — Preview. An A1-addressed spreadsheet grid whose cells hold literals or =formulas, evaluated live by Loom's own pure formula engine. Azure-native — no Microsoft Fabric.

What it is

Sometimes an analysis is a spreadsheet, not a query. A fusion sheet is a 20-row × 10-column grid (A1 through J20) addressed the way every analyst already expects. Cells hold either a literal value or a formula starting with =. The engine evaluates the whole sheet on every edit, resolves cell and range references, detects circular references, and reports Excel-style errors.

When to use it

  • A small model, ratio table, or hand calculation that belongs next to your data items rather than in an emailed workbook.
  • A scratch pad for arithmetic during an investigation, saved with the workspace.
  • For anything that needs to query a backend, use an Analysis board, SQL Lab, or a Notepad query block instead — the fusion sheet engine is a pure calculator over its own cells.

Step-by-step in Loom

  1. Create the item. + New item → Fusion sheet. The editor opens with a Preview badge and an empty grid with column headers A–J and row headers 1–20.
  2. Enter values. Click a cell to edit it. Type a literal, or start with = for a formula. Enter commits, Escape cancels, and clicking away also commits. Clearing a cell removes it from the sheet.
  3. Write formulas. The engine supports:
Function Purpose
SUM Total of cells or ranges
AVG (or AVERAGE) Mean
MIN / MAX Extremes
COUNT Count of numeric values
IF Conditional
ROUND Rounding (optional decimal places)
ABS Absolute value
CONCAT String join

References may be single cells (B2) or ranges (A1:B3), for example =SUM(A1:A10) or =IF(B2>100, "over", "under"). Arithmetic operators + - * / ^, comparison operators = <> < > <= >=, and parentheses are supported. 4. Read the results. Each cell displays its evaluated value; hovering shows the underlying literal or formula as a tooltip. Cells that fail evaluation render in red with an Excel-style error value: #REF!, #DIV/0!, #VALUE!, #CYCLE! (circular reference), #NAME? (unknown function), or #ERROR!. 5. Save. Save persists the cell map to the item's state; a caption confirms Saved. or Save failed. honestly.

The backend it rides on

  • Evaluation: Loom's pure fusion-sheet-engine — it runs in the browser over the sheet's own cells. There is no external calculation service and no data-plane call.
  • Persistence: PATCH /api/items/fusion-sheet/<id> writes state.cells; the editor loads it back from the item store on open.

Honest gates

There is no infrastructure gate on this surface — the engine is pure and the only backend call is the item-state save. A failed save reports "Save failed." rather than silently discarding your work.

Limits (stated honestly)

  • Fixed 20 rows × 10 columns (A1–J20).
  • The function set above; no external data references, no charts, no formatting.
  • Tagged Preview.

No Fabric required

Pure client-side evaluation plus the item store. No Fabric capacity, workspace, OneLake path, or Power BI workspace is involved.

Learn more

  • Analysis board editor tutorial: editor-analysis-board.md
  • Notepad editor tutorial: editor-notepad.md