The "mark up" feature is used by some companies to take their P/Os and use them as a basis for a T&M or service billing. This is done by creating a special form that looks like a P/O form, but marks up the line items instead of showing them in their discounted form.
There are special fields for price, UM, and extension that can be inserted on the P/O form that show the markup amounts. These fields are used instead of the normal fields when printing the form. The original P/O remains untouched -- only the printed form shows different amounts.
For the markup price, extension, and P/O total fields use fields 56, 57, and 58 respectively.
Lastly, you need to tell Apex how you want to mark up the P/O amounts. This is done using a Markup mask commands. (For more information about mask commands see the Apex help file under the "Designing a Purchase Order" apendix.)
Using the Markup mask command you specify the markup percentage, and optionally an "ALL" parameter. If ",ALL" is not specified then the markup price is either the Column 3 price (for DB Items), or for write-in items it is the price entered on the P/O marked up by the percentage specified. If ",ALL" is specified then all P/O lines are marked up by the Percentage amount.
This is a powerful feature, but it is probably one of the more complex features in Apex. Vulcan Software will, of course, be happy to help you set up a special form if this is something that you would like to do.