All Adama probes are now included in the Sader Method - Global Calibration Initiative. This allows you to calibrate each probe by measuring only the resonance frequency (f) and quality factor (Q). Just go to sadermethod.org and enter these two numbers in the @LDV entry for your product and the spring constant will be displayed along with an error estimate. This is the most accurate method available for you to get the spring constant for your products and typically allows < 5 % uncertainty.
The spring constant (k) is determined by the formula
k = A x Q x f^1.3
where A is given by your probe model.
As highlighted in : Nature Nanotechnology, 11, 578 (2016)
API interface : github.com/SaderMethod/API