"Err" parameter in adaptmesh

I try to make a comparison between the adaption with the command “adaptmesh” (that use the hessian method) and one that use the recovery-gradient method with zienchiewiz-zhu estimator (developed by myself).

But i don’t understand exactly what “err” parameter indicates in adaptmesh.

In the second case i set the “tol” parameter as the approximation of the H1-seminorm of the discretization error, and i would like to set the same also in the first case.

And if i want to set the number of elements (and not the error) during the adaptive procedure? Is it possible?

Thanks in advance for any help!