> 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-null.md).
# Null pressure curve
## Introduction
The null pressure curve is the most important pressure curve - exactly because it does nothing. We can apply the null pressure curve to any pressure profile, and it will not shift the profile in any direction.
## Definition
The definition of a null profile is a pressure curve function that takes the input logical pressure and returns that very same value as the output logical pressure. In other words, f(p) = p.
If you take the range of input logical pressures, which range from zero to one, and plot them on the X axis of a chart, and then you apply the null pressure curve to those values and plot the result of the function on the Y axis, then you get a straight line at 45° that goes from the lower-left corner to the upper-right corner of the chart.
Any time you see a chart like this, it clearly identifies the null pressure curve. And you can be sure that it does not do anything to a pressure response.
In the chart above, you can see there has been no change because the orange line, which represents the pressure response after applying the curve, has exactly the same shape as the original pressure response.
## Null pressure curves are extremely useful
We encounter pressure curves in tablet drivers and in creative applications. These kinds of applications often use the null pressure curve as the default value for any pressure curves they have. This isn't always true, but it is a very common thing to see.
If you're ever trying to solve some problem with the pressure of your pen, then knowing about the null pressure curve is useful. It might be that your pressure curve was somehow modified and is affecting your pen. So a very common troubleshooting tip is to make sure that your pressure curve has been reset back to the null pressure curve. This way, you can be sure it is not affecting what is going on.
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