This is s_xx and it is the StdevXCal2*(N-1)
s_xx =(140 ppm)2 . (7-1) = 117,600 ppm2
This is the unknown signal minus the average of the calibration signals, squar
〖(y_0-y ̂)〗^2= (550mV – 300 mV)2= 62,500 mV2
Here is the whole ball of wax to type into your calculator