These define the extent of the computation window.
In both cases, the grid will be created by adaptive refinement.
The mesh density is defined by the maximum memory allowed for the process. The computation time is directly related to the memory, so a lower mesh density (lower memory) will run faster.
Calculations requiring less than 0.5GB can be run on the host almost immediately. However, to keep the host from being bogged down, any calculations that run for longer than 3 minutes will be terminated. If the calculation is expected to run longer, it can be run on a separate computing node. This can be indicated by checking the box "Run on a new node". Jobs that require more than 0.5GB will automatically run a new node regardless of the checkbox indication. Launching a new node takes 4-5 minutes to boot-up and initialize.
The mesh will be refined after the first iteration, and after every indicated iteration (typically 5). Re-meshing after every iteration can lead to instability.