A calibration process is getting a measurement from an alternative
measurement system that is characterized better than your own.  The
problem is therefore to measure the same deflection with two systems at
once, or to have a reproducible deflection that you can measure
consecutively with two different instruments.  Without knowing exactly
how your measurement setup is arranged, and what surrounds your
cantilever beam, the problem is ill defined.  Please describe your setup
in more detail.

Alex