Formula Usage

Sentio dashboards allow you to apply formulas to metrics displayed in charts, enabling calculations like ratios, sums, differences, etc., directly in the UI.

Aggregate Before Calculating Between Metrics

Problem: You want to display the difference or sum of two related metrics (e.g., metricA - metricB or metricA + metricB), but the result seems incorrect or the formula fails.

Cause: Formulas often operate on a single time series at a time. If metricA or metricB (or both) have multiple series due to different label combinations, applying a simple A - B formula might not work as expected because the system doesn't know which series of A to subtract from which series of B.

Recommendation:

1. Apply Space Aggregation First: Before applying formulas that combine different base metrics, ensure each metric involved is aggregated down to a single time series using appropriate aggregation functions in the dashboard UI.
2. Use Aggregation Functions: Select functions like sum, avg, min, max, or last in the metric query builder for each metric (metricA and metricB) to collapse their potentially multiple series (based on labels) into one aggregated series.
3. Apply Formula: Once both metricA and metricB are represented as single, aggregated time series in your chart setup, then apply the desired formula (e.g., A - B).

Example Visualization (Conceptual):

Imagine metricA has series for token=USDC and token=DAI, and metricB also has series for both tokens.

• Incorrect: Directly applying formula A - B. The chart doesn't know if it should calculate USDC_A - USDC_B, DAI_A - DAI_B, USDC_A - DAI_B, etc.
• Correct:
  1. Add metricA to the chart, apply aggregation sum (let's call this aggregated series SumA).
  2. Add metricB to the chart, apply aggregation sum (let's call this SumB).
  3. Now apply the formula SumA - SumB. This calculates the difference between the total sum of A across all its series and the total sum of B across all its series.

(Based on original best-practice/formula-usage-best-practices.md)