Facebook has come a long way since it’s first ad placements: banner ads called Facebook Flyers that allowed advertisers to target college students with a specific school’s .edu email address. What’s happened since mirrors the marketing developments we’ve seen across the web. Technology has led to more effective advertising as well as improved tracking and retargeting. But Facebook, with its vast trove of personal information, is now stepping into relatively unknown territory as it introduces a vital improvement to its Custom Audiences ad tool, and paves the way to offline sales attribution. This could change the world of advertising. Custom Audience Measurement works like this: businesses collect email addresses of their customers. The businesses then submit the email list in an encrypted, privacy-enabled manner, and advertise to those people on Facebook. When a customer makes a purchase at the advertiser’s store location and swipes a credit card, loyalty card, or provides their email address again, the businesses can match purchases to email addresses. The data is then compared (again, encrypted to protect privacy) and Facebook reports the information to the businesses, comparing advertising exposure, clicks, and sales numbers.