Device parameters (tags)

A tag (parameter) is one named measurement on a device — temperature, voltage, flow_rate. Each device has one or more tags.

When you add or edit a device you define its tags, each with:

• a name (the key the device/gateway publishes),
• optional unit (°C, V, L/min) shown on widgets,
• optional scaling — a factor (multiply or divide) and an offset (see below),
• optional min/max for gauges and thresholds,
• optional sound alert for threshold notifications (see sound alerts).

Widgets and rules reference a device + tag pair. If you change a tag's name later, re-point any widgets that used it.

Scaling: factor (multiply or divide) and offset

Many sensors report a raw number that isn't the real-world value — a Modbus register might hold the reading in hundredths, or an analog input might report a raw count. A factor and an offset convert that raw reading into a real (engineering) value.

Choose the direction with the Multiply / Divide switch:

Multiply:  displayed value = raw × factor + offset
Divide:    displayed value = raw ÷ factor + offset

• Reading a Modbus datasheet? Vendor docs almost always give a scale factor to divide by — e.g. "the register stores the value ×10" means divide by 10. Just choose Divide and type 10 exactly as the datasheet lists it. (You don't need to invert it to 0.1 yourself — the platform does that internally.)
• In Multiply mode the factor can be any positive number — greater than 1 (e.g. 100) or less than 1 (e.g. 0.01, 0.001). A register that holds hundredths of an amp is either Multiply 0.01 or Divide 100 — both give the same result.
• The offset is added after scaling — use it for sensor bias or a fixed baseline. Leave it 0 if not needed.
• The default is Multiply, factor = 1, offset = 0 (the raw value is shown as-is). A live example under the inputs shows exactly how your numbers are applied.

The platform stores the raw reading and applies the factor and offset for display, so you can adjust them later and every chart — past and present — re-scales. Alert thresholds are entered in the displayed (scaled) value, not the raw one — see alert thresholds.

You can change a tag's scaling or its alert threshold at any time from the device's Edit form — no need to delete and re-add the tag. Open the device, find the tag, and use Edit scaling (or Edit threshold).