Some points on a jobsite are more expensive to miss than others, and tie-in points sit near the top of the list. A tie-in is where new work has to marry existing work — new steel to a standing structure, an addition to a foundation that's already there, one pour meeting another. The plan assumes those points are where the drawing says. When the survey that located them was soft, the misfit doesn't show up until two pieces are supposed to connect and don't.
A tie-in has no tolerance to give
On open layout you often have a little room — a point can be a hair off and the next operation absorbs it. A tie-in is the opposite. The existing side is already built and can't move. The new side was fabricated to the plan. The only thing standing between "it bolts up" and "it doesn't" is whether the point where they meet was located correctly. There's no slack left to spend.
Tie-ins tend to live on the hardest geometry
Here's what makes it worse: tie-in points are very often corners and edges — the corner of an existing footing, the edge of a wall, the outside face where a new frame lands. And corners are exactly the geometry that's hardest to shoot cleanly, because there's no surface at the actual point to hold a prism on. So the most unforgiving point on the job is also the one most likely to get an eyeballed offset. That combination is where field misfits are born.
Locating it so it actually ties
The way to protect a tie-in is to take the guesswork out of the offset — to capture the corner or edge from a fixed, known reference so the point you hand the detailer is one they can build to without a fudge factor.
The Precision Corner Offset (PCO-1) does that for any outside 90° corner a tie-in lands on. Seat the corner in the 90° pocket, mount your mini-prism, and store the point at a known 1", 2", or 3" offset. The true corner backs out of fixed geometry, and — just as important — every crew member captures it the same way, so the tie-in you record means the same thing to the person fabricating to it.
The takeaway from the dirt
A tie-in point is a promise: build to this and the new work will meet the old. Keep that promise and the connection drops together in the field. Break it with a guessed offset on a corner nobody could shoot cleanly, and you've moved the problem downstream to the worst possible place to discover it.
The Precision Corner Offset locates outside corners and tie-in points at a selectable, known offset on a standard 5/8-11 mini-prism mount — ASA frame, 6061-T6 aluminum corner plates, made in the USA. See the specs →