In the following demonstration of integer subtraction, the minuend and subtrahend are modeled by using[br]small blocks marked with 1 or -1. [br]Press the gray buttons to form a positive or negative minuend and the green buttons to form the subtrahend. 

Many thanks to [url=https://www.geogebra.org/u/orchiming]Anthony OR 柯志明[/url] for bringing the following article to my attention and for his valuable suggestions.[br][br][u]Reference[/u]  [br]Kaner, P.A. (1964) 'The addition and subtraction of negative numbers', [i]The Mathematical Gazette[/i], [b]48[/b](364), 183-185. [url=https://www.jstor.org/stable/3613541]https://www.jstor.org/stable/3613541 [/url]