This keyword defines the value of the 
at which the calculation will stop. Normally
this is equal to the number of observations. If you want to stop earlier (a more uniform map),
or later (a more peaky map), you can achieve this either by changing the TARGet, or
changing the standard deviations of your measurements. I should warn you, however, that both
procedures are probably wrong (and dangerous), unless you have reasons to believe that
the standard deviations of your measurements are incorrect.