I tried the same using event router for building similar calculator application, but i see that the output is not getting changed on every click.
below image for reference when i tried.
In the above image for button 1 & 2 click the context id mapped with same 1 & 2 are not getting displayed in the output text box, but if i write anything on the other two text boxes and on leave from the text box, i am able to see the same in the output text box.
what am i missing in the button that i am not able to see the respective context ID in the out put text control on click ..???