Great kata, thank you )))

I can't understand jnz. If "Note: The jnz instruction moves relative to itself. For example, offset -1 will continue in the previous instruction, and offset 2 will skip the next instruction", why
"mov a -10",
"mov b a",
"inc a",
"dec b",
"jnz a -2"
result {"a", 0}, {"b", -20}? Why b != -11?