Put units in the ledger first
Imagine one hour with 12.0 BTC in base volume, 1,200,000 USDT in quote turnover and 800 trades on exchange A. These invented values summarise different aspects of activity. Adding them produces no meaningful common unit.
If exchange B reports 8.0 BTC for the same spot instrument and interval, the selected two-exchange total can be 20.0 BTC. It is not automatically global volume. State which venues were included and omitted.
Read the provider's field definitions
Binance spot data distinguishes base volume, quote volume and trade counts. In BTCUSDT, those first two units are BTC and USDT. Do not infer field meanings from their position in another API.
OANDA defines candlestick volume as the number of prices created during the interval. It cannot be compared directly with BTC traded quantity to claim that one market had several times the trading volume.
Align the aggregation window
A rolling 24-hour statistic need not cover the same window as a fixed daily candle. Match start, end, time zone and instrument type before selecting comparable rows.
A reusable record format
Provider / symbol / market type / start / end / field name / value / unit / exclusions. Mark unknown fields as unresolved rather than filling them with assumptions.