Charting history with spreadsheets

Build pivot charts, rolling minimums, and dual-axis humidity plots from exported garage CSV files.

The built-in dashboard charts answer everyday questions. Spreadsheet charting answers audit questions: “How many hours below 35 °F last January?” or “Did humidity correlate with door events?” Exported CSV from CSV export is the starting point; good column hygiene makes charts fast to rebuild when new data arrives.

Spreadsheet with timestamp column and line chart of two probe series
Pivot tables and line charts turn exported CSV rows into custom freeze and humidity analyses.

Import hygiene

  • Parse timestamps as datetime, not text—sort ascending before charting.
  • Split probe_key into separate series rather than one blended line.
  • Keep Fahrenheit and Celsius columns consistent; pick one axis unit.

Useful chart types

  1. Rolling 24h minimum temp per zone for freeze planning.
  2. Dual-axis temp and humidity to spot condensation risk windows.
  3. Week-over-week overlays after insulation upgrades.

Correlate external data

Merge weather API CSV on aligned timestamps—see weather API parallel path. Mark manual events (door open, car parked) in a helper column to explain spikes from door swings or vehicle heat.