It does not allow for "Intermediate or Chain Calculations", i.e., you can not perform the following without pressing the equal sign after each operation:

Example: "3 * 2 * 4 + 5 = " IS NOT Allowed.
You must operate on the expression as follows: " 3 * 2 = 6 * 4 = 24 + 5 =29 "

You will notice that the * ; / ; + and - operators are un-enabled after one is pressed and that the " = " blinks.
So you must select the " = " sign to finish the current operation prior to moving on to the next.