"We keep the URL the same and update the content. That way, there are no broken links," says Sutton-Gee. "When a user clicks on the plan or detail, a drop- down menu appears that shows the most recent version as well as past iterations."

Wesling says he worried that site plans would be hard to view on an iPad screen because the screen is not the size of a full plan. "But navigation is so fast—jumping around and zooming in on details—that it works well," he says. "We love it."

The vendor says developing the auto-linking was a challenge. "Our machine-learning algorithm is quite a bit more computationally complex than anything we have done before," says Cory Lorenz, vice president of research and development for PlanGrid.

The process is so complex, Sutton-Gee hasn't even filed for a patent yet. However, he says he is not concerned someone will steal the idea."Its very non-obvious how we have done it. It's quite difficult," says Sutton-Gee.