Is it possible while drawing a line or measuring the length with a tape divide active length? Because typing “/” symbol in measurement value cleaned actual length data. So the only way is to rewrite the length again and add a divide operation.
The slash would only be used in this way with the Move or Rotate tools. What exactly are you trying to achieve? Can you show us an example?
see measurments bar
As I wrote before, the way you are trying to use the slash is restricted to the Move and Rotate tools. It isn’t supposed to do what you are trying to do. You could draw the line between the boxes, then right click on it and choose Divide. Divide the line in two segments and erase one of them.
got it, thanks 
The other way to do this is to use the tape measure tool to place a perpendicular axis line at the start of the length that you want to divide. Then with the Move tool (M) active use the Command or Option key to select and copy the axis line. Drag the copy to the end of the length you want to divide. Once placed then use the “/” numerical value you want to divide the length by.