As an example, on a J/70, with the jib furled in medium wind, it's about 1-to-1. So if you tack at 60 seconds to the gun and 200 feet from the line, and you cruise with the main only, that ratio will be going down another 3 feet per second. If you did nothing, you'd start at 0 seconds, right on the line, but with the jib furled. Of course you'd never do that. Instead, tack at 260 feet and 60 seconds, giving you 65 extra feet to work with. Now you're marching toward the line, and the feet and seconds are still reducing at about 1-to-1. You're watching them both go down as you're managing your east-to-west spacing, making sure you have a hole to leeward, and dealing with threats from other boats. You know from practice runs on the start that your speed doubles when you deploy. Somewhere around 10 to 15 seconds, deploy the jib and start going 6 feet per second instead of 3 feet per second. If you get it right, you nail the start—3 to 6 feet back from the line, at full speed and close-hauled.