> For the complete documentation index, see [llms.txt](https://docs.sevenpens.com/drawtab/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.sevenpens.com/drawtab/core/pressure/pen-pressure-curves/pressure-curve-constrain-output.md).
# Constraining pressure curve output
## Overview
Typically, a pressure curve function takes input logical pressure values in the range of \[0,1] and maps it to values in an output range of \[0,1]. This means that the full output range is used.
Some curves can limit their output range to achieve better control over brush strokes.
## Visual interpretation
The easy way to tell that a pressure curve constrains the output range is to notice that the curve shape does not reach the bottom or the top of the pressure curve graph. Two examples are below.
Even though the shapes look a little different, they both effectively take the input logical pressure values between \[0,1] and map them to an output region close to \[0.3, 0.6].
## Impact on brush strokes
Imagine the user's brush setting is 100px and the brush is set to change its size in response to pressure. Then suppose the user draws a stroke that goes from the IAF value to the MAX physical pressure.
The stroke size is computed like this:
```
pressure = apply_curve( pressure )
brush_size = max( 1, 100 * pressure )
```
* With a null pressure curve, the stroke width will go from a size of 1 px to 100 px.
* With the curves shown above, the stroke width will go from 30 px to 60 px. So the width of the stroke does not vary as much.
## Use cases
* Helps give you more consistent brush strokes while still allowing some variability
* By avoiding the lower end of output logical pressure, you can have your strokes start off a little thicker than normal. (Though some apps have other ways of accomplishing this goal.)
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