Round turn

A counting convention rather than an event. Every position involves two executions, and a charge or a statistic can be expressed against either one of them or against the pair. Quoted per side, a figure covers a single execution and applies again at the close. Quoted per round turn, it covers both. Futures exchanges conventionally report volume in round turns, so a published contract volume is half the number of executions that produced it. Both conventions appear in the same documents, in the same font, and commission comparisons collapse whenever the basis is not checked.

The conversion is trivial and is exactly where the error lives: a per side figure doubled is the round turn figure, and a round turn figure halved is the per side one. A charge that looks twice as expensive as another is frequently the same charge described the other way. Where a charge is expressed as a percentage of notional value rather than per lot, the same question applies before the two can be compared at all, since a percentage of notional and a fee per lot are different bases as well as different numbers.

The larger trap is treating a round turn commission as the cost of a trade. It is one of three charges. The spread is paid on entry and again on exit, commission is charged on the basis above, and any financing accrues for as long as the position stays open, so only the sum of the three describes what a position cost. Comparing two pricing models on the commission line alone reliably produces the wrong answer, because the model quoting no commission has recovered its charge inside the price instead.