Hi Overson
When you say you can only change between 8-12.
The way i have read it is that the marker has 5 dwell settings. 1-5 which correspond to what dwell you require.
i would set it to 3 (10ms) as that is the default and go from there.
If its warm maybe drop it down a little 1 or 2
If its colder maybe raise it up a little 4 or 5.
I Hope i have got the idea of what you ment and this is of use to you.
If not let me know.