# Understand Math Done For Endpoint In Canvas Arc

## 10 January 2016 - 1 answer

Given that i want to draw a circle in canvas that looks like below: Now i am using the circliful plugin ,

Now the math done behind the scenes is like so:

``````if (type == 'angle') {
startAngle = 2.25 * Math.PI;
endAngle = 2.4;
circ = 1.53 + Math.PI;
quart = 0.73 + Math.PI / 0.996;
}
``````

The above math gets used like so:

`````` context.arc(x, y, radius, endAngle, startAngle, false);
``````

Now i understand the math done for startAngle, but why `endAngle = 2.4` ? where does the `2.4` come from ?

I know it works perfectly, Why 2.4 ? can anybody explain ?

The line of code can be seen HERE.

The `context.arc` function takes angles measured clockwise from positive x. With other words, the 2.4 indicates approximately going from the center to the bottom left at a 45 degree angle.
Similarly in the same code there's a snippet that says `endAngle = 3.13`, which is nearly PI or nearly 180 degrees (so pointing to the left), that's used for half a circle.