There are several ways to calculate the value of the arctangent. One of them is known to us from school - are the tables Bradis. Sometimes, in the field, this may be the only one.
Another way is to use a standard calculator Windows. To do this, first switch to advanced mode - in the menu, under "View" select "Engineering" and then the function buttons in the calculator will significantly increase.
Then enter the value of the arc tangent from which you need to calculate - you can do it from the keyboard, and clicking the right keys on the calculator with the mouse, and just copying and pasting the desired value (CTRL + C and CTRL + V). Then select the type of units in which you need to answer (in radians, degrees or rads) - this is done by choosing one of three possible values for the switch under the input field calculated value. Then check the box that says "Inv" - it reverses trigonometric operations. Now by pressing the button labeled "tg", you will get the value of the function, the inverse tangent, i.e. the desired value of the arc tangent.
And, of course, in the Internet age, the network can not exist online offering to solve this problem online. Online calculators have user-friendly interface and more advanced compared to the standard Windows calculator features - for example, it is possible to calculate not only the value of one function, but the expression of several functions.