C2A gives you the ability to get an histogram of magnitude for all the stars visible in the sky at a certain location and at a certain date and time. To get the histogram, just use the command Magnitude Histogram... from the Tools Menu. You will then get a small windows that gives the values for the histogram, i.e. the number of stars in different classes of magnitude:
You can specify the minimum altitude for the stars to be taken into account. The Refresh button allows you to update the histogram in case the minimum altitude has been changed or when a significant lapse of time has passed. Finally, the Histogram button lets you display a graphical view of the histogram assuming the Python 3 environment is installed on your computer. If it is not the case, an error message is displayed. See the section devoted to the Python 3 environment to see how to install and use Python 3.