Copy trading looks simple from the outside: the master trades, the followers trade. The reasons implementations differ in quality sit entirely in the details of how that translation happens.
Step 1 — Subscription
A follower selects a master and sets an allocation: how much of their account is committed to following that strategy. This allocation is what every subsequent sizing decision is computed against.
Step 2 — Observing the master
The system watches the master account for trading events — position opened, position closed, position partially closed, order modified. Each event becomes a task to apply across the follower set.
Step 3 — Proportional sizing
Each follower's position size is computed from the master's volume scaled by the ratio between the follower's allocation and the master's account. A follower with one percent of the master's capital takes roughly one percent of the volume, subject to the minimum volume the instrument permits.
Minimum volume is a real constraint. Below a certain account size, proportional sizing rounds to less than the minimum tradable lot, and the system has to either skip the follower or round up — which changes their risk. A good implementation makes this explicit rather than silent.
Step 4 — Reconciliation
Every operation either succeeded or did not. The system must record which, and surface the failures.
The right-hand column is not exotic. It is simply what an honest system does, and the difference between the columns is the difference between a product and a liability.
See the follower and master views
The demo shows both sides of a copy relationship on sample data.