The above equation is called the Biot-Savart law. However, the current must form a loop. You will not have only a small current element. There is no magnetic field in the direction of the current element.
P is due to current elements from two yellow line sections.
Now we have a way to measure the magnetic field just due to one current element. The point P moves when you make the above changes. P is shown at the top left corner. Click at the DC current source to change its polarity. You can enter value for the current source into the text Field.