> ## Documentation Index
> Fetch the complete documentation index at: https://docs.farelint.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Historical observations

> Compare prices across time without losing their identity.

`GET /v1/observations` is the proposed interface for retained observations. There is no comprehensive historical archive available today.

## Two different dates

**Observation time** tells you when a fare was collected. **Travel date** tells you when the passenger would fly. Keep these independent in your queries and charts.

## Compare like with like

A comparison should match carrier/source, airports, departure and return dates, passenger mix, cabin, market, original currency, price basis and available fare conditions. Different departures or baggage allowances are different series.

## Preserve the original price

Amounts are decimal strings. Retain original currency even when providing an optional converted display price. A conversion needs the rate, rate date and source. Exchange-rate movement is not an airline price change.

## Retention and completeness

Your agreement defines retained sources, dates, fields and delivery method. Queries should expose coverage start/end and collection gaps. A missing observation is not proof that a route had no flights.

Historical data can support your own trend analysis. A low current observation alone does not prove a market discount or seasonal pattern.


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