3. Compass Record Selection — Linear Gauge
In this step you select the Compass record that the Linear Gauge widget will use. Your record must return a single row with a single numeric value.
Wizard route: /cartography/add/selectcompass
1. Compass Record List
2. Suitable Record Structure for Linear Gauge
-- Tank fill ratio
SELECT tank_fill_percent
FROM tank_status
WHERE tank_id = 1
ORDER BY ts DESC
LIMIT 1;
| Column | Role in Step 4 | Type |
|---|---|---|
| Single numeric column | Value Source | NUMERIC |
Single Row Is Mandatory
If the query returns more than one row, the gauge uses only the first row. Guarantee this with LIMIT 1.
3. Compatible Data Sources for Linear Gauge
| Data Source | Linear Gauge Compatibility |
|---|---|
| MQTT (live) | ✅ Ideal |
| PostgreSQL / MSSQL / MySQL | ✅ Suitable |
| REST API | ✅ Suitable |
| Excel Offline | ⚠️ Limited |
4. Search and Tag Filter
| Action | Effect |
|---|---|
| Search box | Instant filter |
| Tag filter | Only tags in use |
| Clear | Reset filters |
5. Confirm the Record
When you click a record the row is highlighted. Click the Next button at the top right to proceed.
Proceeding Without Selecting a Record
If no record is selected, Next gives a warning.
6. Excel Offline Sheet Selection
For Excel records, an additional Sheet dropdown appears.
7. Preview Execution
When you press Next, the record is executed and the result is held in memory.
8. Common Errors
| Symptom | Likely Cause | Resolution |
|---|---|---|
| Gauge shows value 0 | Empty row | Test the record in Compass |
| Multiple values | LIMIT 1 missing |
Add LIMIT 1 to SQL |
| Value Source dropdown empty | No numeric column | Return a numeric column with CAST(... AS NUMERIC) |