The word "sale" is used two ways in Manifold, and they are separate features. Which one you want depends on what you are asking.
**A sale as something you sold.** One transaction: an invoice with a customer, lines and a total. This is the sense in every "sales" report, in commission and spiffs, and in the pipeline. If you are asking who gets credit for a deal, how much the shop sold last week, or how a split works, this is your sense. See How to Create an Invoice, Splitting a Sale Between Two Salespeople, and the salesperson reports.
**A sale as a promotion.** A percentage off part of your catalogue between two dates: 20 percent off Rockford Fosgate speakers for a week. You set these up under Point of Sale > Sales, and Manifold prices invoice lines from them while they run. If you are asking how to take a percentage off for a while, this is your sense. See Running a Sale, How Overlapping Sales Combine, and How to Use the Sale Performance Report.
**Two other ways to take money off, which are neither of those.**
- A discount line on a single invoice, added with + Discount. It affects that one document and nothing else.
- A birthday or anniversary special, which is offered to one customer around their day. See "Birthdays and anniversaries: texts and specials".
A rough rule: a promotion is set up in advance, applies to everybody, and has dates. A discount line is one person, one invoice, right now.