Chalking in Hermann eggs and when to give up?

[Patti]

Hi, my 8 Hermann eggs have been incubated for almost four weeks, temp 31-32 degrees and 75% humidity.

I've candled three times at weekly intervals.
No sign of the ring of life or veins but all the eggs are continuing to chalk. Some, just the base or tips are left to chalk.

I haven't been a member long enough to post photos yet.

Is it time to switch off the incubator?