|The difference lies in the context in which the two are
used. Scans operate on current data, and can be used to:
- Find symbols within a given quotepage (and periodicity) that match
a given criteria, or...
- Set properties or V# variables for all the symbols in a given
A scan is sometimes called a "screen". A scan can either be run
manually by the user, or be scheduled to run periodically. For
more information on scans, visit the
the scans tour, or
view some scan examples.
The scan interface is very similar to the signal interface except it has
several additional controls/settings. Periodicity ("Period") and
quotepage ("QP:") options dictate the symbols and the timeframe of data
on which the scan will run. A format option dictates the columns
that will be present in the resulting quotepage (which shows all the
symbols that returned "true" on the scan criteria). Sorting
options allow the user to automatically sort the resulting quotepage on
a given column (either ascending or descending).
Signals are basically true/false expressions that can be used
historically, in charts, trading system, custom columns, etc.
Signals will operate on the periodicity of the chart, trading system, or
custom column in which they reside, and therefore do not need a
periodicity setting within the Signal itself. Similarly, signals
will operate on the symbol in the chart, or the quotepage of the custom
column or trading system, and therefore don't need the quotepage,
sorting, or format options that scans do.
In charts, signals are used within a variety of indicators:
Color Markers, etc. The signal result (true/false) is
evaluated and "marked" for each bar historically. In trading
systems, each trading system rule involves a signal and an action.
The system will evaluate the rule on each bar, and take the resulting
action (buy, short, sell, etc). Often, signals are used in "No Action"
rules to maintain the values of Targets, V# variables, etc.
In many cases, signals and scans can be used interchangeably.
Therefore, a checkbox can be seen in both Scan and Signals windows
titled "Enable this Scan for use as a Signal" (or visa versa).
When that checkbox is checked, the signal will show up in scan lists
(for signals), or the scan will show up in signal lists (for scans).
In a nutshell, scans are used to either find symbols which currently
meet a given criteria, or to set properties (V# variables, etc) of the
symbols in a quotepage, or sometimes both. Signals can perform the
same function, but historically, on each bar.