Slope and intercept calculation incorrect in pHParams.py

[thni323]

In pHParams.py calc_ph_slope() the parameter xy is of the following form:
xy: [ [ph[0], reading[0] ], [ ph[1], reading[1] ]
but linregress would expect the following form:
xy: [ [ph[0], ph[1] ], [ reading[0], reading[1] ]