This is meant to be a fun js Turing Machine Simulator. 

This is an example instruction set for a subtractor:
{1,_}->{1,_,R}
{1,1}->{1,1,R}
{1,-}->{1,-,R}
{1,=}->{2,_,L}
{2,1}->{3,=,L}
{2,-}->{H,_,L}
{3,1}->{3,1,L}
{3,-}->{4,-,L}
{4,_}->{4,_,L}
{4,1}->{1,_,R}

You can try this on the input:
1111-111=