Let's assume for our example that you would like to set the box size to $0.25 for stocks trading under $5, $0.50 to stocks trading between $5 and $20, and to $1.00 for stocks trading over $20. The following scan will accomplish this.
SET(BOX, (CL < 5) * 0.25 + (CL >= 5 AND CL < 20) * 0.50 + (CL >= 20 * 1.00))
The token "BOX" refers to each symbols Box Size. "Box Size" is also a column that you can add to any quotepage and adjust manually. Both Point and Figure charts, and the Point and Figure technical indicator, have an option to "Use Box Size of Instrument". When this checkbox is checked, the instrument's box size (which can be set using the scan above, and seen/adjusted in the "Box Size" quotepage column) will be used instead of the specific box size given in the preferences. As you switch symbols in the chart, the box size will switch to reflect the box size of that symbol/instrument.