This is a 4 bit adder (obviously). This is a really low-grade calculator that cannot add numbers larger than 16 (in binary). If you want to check the validity of the calculator, here is a list of values for binary.

1 = 0001  ,   4= 0100  , 7=0111     ,  10 = 1010

2= 0010   ,  5= 0101   ,  8=1000    ,  11= 1011

3= 0011    ,  6= 0110   , 9= 1001    ,  12= 1100