Custom symbol

A custom symbol is an instrument defined inside the platform by the reader rather than supplied by the broker — built from imported price data, or derived from instruments the broker does quote. It appears in the platform's instrument list and can be charted and tested against like any other. What it generally cannot do is be traded, because no broker is quoting it: there is no counterparty behind a symbol that exists only on one machine. Everything about it is also an assertion by whoever created it. Its contract terms, its unit of price movement and the costs modelled against it are whatever was typed in, and the price history behind it is whatever was imported. That makes a custom symbol a useful way to look at a series that is not offered directly, and a poor thing to compare against a broker-supplied instrument, because none of the figures came from the same place.