  We demonstrate how dispersive atom number measurements during evaporative
cooling can be used for enhanced determination of the parameter dependence of
the transition to a Bose-Einstein condensate (BEC). In this way shot-to-shot
fluctuations in initial conditions are detected and the information extracted
per experimental realization is increased. We furthermore calibrate in-situ
images from dispersive probing of a BEC with corresponding absorption images in
time-of-flight. This allows for the determination of the transition point in a
single experimental realization by applying multiple dispersive measurements.
Finally, we explore the continuous probing of several consecutive phase
transition crossings using the periodic addition of a focused "dimple"
potential.
