dart glitch?

[yesketchup]

so i pressed all buttons but it does not work, not even sure what the result is supposed to be. i solved this puzzle so many times before, but now nothing..
screenshot: https://gyazo.com/1288351ada30e6e70b9511de74e03b90

[gunquinn]

18 - 16 = 2
2 squared (2 X 2) = 4
Answer should be 4