In the hypothetical order book below, buying two coins costs 202USDT even when the best quote is 100. Before judging a signal, you need the quantities and prices that actually filled to calculate your own profit or loss. For someone considering automated orders, the first comparison is also the signal price against the average fill price.
Why can the price fall while people are buying?
A public question posted on 12 October asks how Bitcoin can fall while buyers are present. Start with the price at which orders meet, then distinguish a trading signal from a fill. The order book and signal rule below are illustrations, rather than a reconstruction of the market or a Whalehunter operating signal.
Each completed trade has a buyer and a seller. Suppose the last trade was 100 and bids remain at 100, then 99. If a sell order consumes the first quantity and trades with the buyer at 99, the new execution price falls. The presence of buyers alone does not tell you whether orders willing to pay more remain.
Two coins shown at 100: why pay 202?
Assume this fictional COIN/USDT sell-side order book. No other orders arrive, no order restriction intervenes, and all two coins fill. Fees are excluded for now.
| Ask price | Quantity offered | Quantity bought here | Amount paid |
|---|---|---|---|
| 100USDT | 1COIN | 1COIN | 100USDT |
| 101USDT | 0.5COIN | 0.5COIN | 50.5USDT |
| 103USDT | 2COIN | 0.5COIN | 51.5USDT |
| Total | — | 2COIN | 202USDT |
The average fill is 202÷2=101USDT. That costs 2USDT, or 1%, more than the 200USDT estimate obtained by applying the best ask of 100 to both coins. This calculation consumes hypothetical available quantities; it does not establish an exchange guarantee of either price or quantity.
Real quotes can change and an order can fill only partly. Bybit's spot trading rules explain that price limits can leave a market order partly filled with the remainder canceled. Add the filled quantities and amounts paid before calculating the average.
Observation, signal, order and fill need separate records
For a separate example, define a rule: consider buying when a completed candle closes above 105. A high of 106 with a close of 104 fails it; a close of 106 meets it. This is a different illustration from the order book above. Passing this rule does not demonstrate profitability or successful order execution.
| Stage | What to record | Difference from the next stage |
|---|---|---|
| Observation | Asset, market, candle interval, close time, price | An open candle differs from a closed one |
| Signal | Rule, qualifying time, invalidation condition | A signal creates no holding by itself |
| Order | Side, type, quantity, price ceiling, order ID | Submission and acceptance differ from a fill |
| Fill | Individual price, quantity, time, fee currency | Include partial fills and the canceled remainder |
Repeating a rule requires more detail than “buy the breakout.” Specify the market and candle, when the order expires, and whether an existing holding permits another order. Giving a program the task does not remove these choices.
A limit order does not always mean a cheaper fee
Bybit's Post-Only explanation says an order that would immediately match the opposite quote is canceled; one resting in the book is treated as maker. A regular marketable limit order can be a taker. “Submitted a limit order” and “filled as maker” therefore need different records.
Bybit's VIP 0 crypto-to-crypto spot baseline is 0.1% for both maker and taker; check regional and account rates separately.
If waiting for a lower fee leaves an order canceled or prevents exiting at the intended time, the rate alone cannot choose the order type.
Complete one line before writing a return
The model produces “2COIN, average 101USDT, paid 202USDT, fee separate.” An actual record also needs the fee quantity and currency, sale fills and remaining holdings. Keep an unfilled signal in the signal log; do not put hypothetical profit into the trading profit field.
Start with your market, quantity and order conditions in the blank trade plan and record. Continue to the exchange fee comparison for round-trip costs, or the first-purchase glossary for price appreciation versus money left after selling.
Sources read on 12 October 2026. Order-book prices, candle prices and the rule are original illustrative assumptions. The official spot rules were updated on 21 July 2026, Post-Only on 17 June, and the fee structure on 2 September.