Odd EGT instrument?

My new (to me!) Comanche has an odd EGT instrument. Across the top,
in blue, it is marked in "% Range" with 60, 70, 80, 90, * and below
that it's marked in white "Ex Temp x100 deg F" with -3, -2, -1 and *.
There's a tiny thumbwheel which can adjust it, though it doesn't have
a lot of authority.

The highest I can make it read at any power setting up to 75% (including
thumbwheel adjustment) and leaning by engine sound/fuel flow is -1.
Should I be able to get it up to '*'?

--
Ben Jackson

http://www.ben.com/