Sizu Riatto
Every Angle · Chapter 9

Vectors and Routes: the Cable

A cable can't fly. Write each run as legs east, north and up, add their sizes for the cable along the walls, and add the vectors themselves for the straight line between the ends.

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Opens on the book's house and plot. Change any number to your own and press Calculate.

One entry hole, low on a wall; each run climbs to the camera's height, then follows the walls

Each run's legs along the walls, as east north pairs in meters (west and south are negative), separated by commas

Enter the heights and each run's legs, then press Calculate.

The formula

  • The climb = the camera's height − the hole's height
  • Along the walls = the climb + the sum of every leg's size (|east| + |north|)
  • The straight line = √((Σ east)² + (Σ north)² + climb²): the vectors added, then 3-D Pythagoras
  • To buy = Σ (along the walls) + slack × the runs; check the longest run with its slack against the 100 m channel limit
  • 1 m = 3.2808 ft; cost = feet × the price a foot
The book's worked example, Chapter 9. Out of one hole 0.3 m up the west wall, each run climbs 2.4 m then follows the walls: runs of 13.4, 20.9, 9.4, 19.4, 3.4 m, 66.5 m along the walls; in straight lines 10.33, 12.17, 7.40, 12.44, 2.60 m. With 1.5 m slack a run, buy 74.0 m (242.8 ft). The longest run is 22.4 m, far inside the 100 m channel limit.
Check it. Before you buy, walk each run with a tape along the walls and add it up: if it is more than a meter over the calculator, a leg is missing.

Honest limits. Corners, clips, drip loops and a route round a window all add length: the slack is a minimum. Outdoor runs need outdoor-rated cable and weatherproof joints; drilling through a wall needs a cable-and-pipe detector first. The book's house was worked out on paper from published figures, not surveyed by us: measure your own, and walk your own plot at night. Prices are illustrative US prices from November 2026, shown without a currency sign; put in your own. Everything stays in your browser: no sign-up, nothing stored.

These calculators go with Every Angle (Make It Add Up, Book 2), where every number on this page is worked by hand.