pwhitt is right. When you include the equation inline with HSEROUT ["0-5=", ~Result+1] you're telling PBP to output the "result" of ~result+1.

And since the compliment is handled as a 16-bit operation, HSEROUT is going to send a 16-bit result computed internally by the inline equation ~result+1.

You can see how this works with something like this;

HSEROUT ["100 * 50 = ", DEC 100*50,13,10]

Note there's no reference to any variable. Only an equation. That's pretty much the same thing as passing ~result+1 to HSEROUT. It's going to print the result of the equation, and not the byte variable result.