Stair curves are used to divide analog input values into discrete steps. For example, the curve below, named "9st" (for "9 step"), will divide an analog source's output value into steps of -100%, -75%, -50%, -25%, 0%, +25%, +50%, +75%, and +100%.

Stair curves are useful during model setup to collect data for use in calibration of curves that are active during control of the model. Uses include calibrating and matching control surface positions, and calibrating elevator-flap compensation curves, which adjust elevator position for level flight at all flap positions. A compensation curve could also correct changes in pitch caused by changes in motor thrust.

**The Ultimate Stair Curve**
Curve "9st" above is a 16-point curve with 9 steps that can be used to obtain the data for calibrating a 9-point curve, but OpenTX supports curves with up to 17 points, and more points can mean greater precision when a curve is accurately calibrated. Single stair curves of up to 9 steps are possible, but I'll show here how to set up stair curves with any number of steps from 5 to 17, enabling precise pinpointing of the default X values for

*Custom X* curves of up to 17 points. For stair curves of 10 to 17 steps, this is accomplished by combining two curves.

Here are the two curves used to create a 17-step stair curve. The first one is named "17P". The "P" indicates that it's applied to the positive half of stick travel:

And this one is named

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