Similar symbols, different units
BTCUSD expresses a bitcoin price in USD; BTCUSDT expresses it in USDT. This site's learning chart selects BINANCE:BTCUSDT and BINANCE:ETHUSDT. It does not establish another exchange's dollar price or an external service's settlement rules.
Convert a hypothetical observation
Assume simultaneous invented quotes of 100,000 USD/BTC, 100,200 USDT/BTC and 0.999 USD/USDT. Multiplying the latter two gives 100,099.8 USD/BTC. The common-unit difference is USD 99.8, or 0.0998% relative to USD 100,000.
Subtracting the original numbers and calling the difference “200 dollars” mixes units. None of these numbers describes a current token valuation or exchange price.
What conversion does not resolve
Check the asset and instrument type, all observation times, providers, and whether each value is a last trade, mid, bid or ask. Fees, transfer times and actual order availability are separate questions. Binance's market-data documentation identifies base and quote assets and distinguishes different price and volume fields.
Separate the calculation from its interpretation
Write “hypothetical common-USD difference: 0.0998%” first. Then list unverified timing, price-type and execution conditions. A numerical difference alone is not evidence of an executable opportunity. Keeping these statements separate makes later corrections traceable.