...
I am forced to conclude that 002 reading higher than 012 in the field is not a calibration difference. Thus, this difference must have been due to spatial inhomogeneity in the soil.
For my records, here is code to plot this:
ref = c(0,7.1,13.8,20.7,28.6)
> e01 = c(-3.14,3.71,15.87,21.05,25.33)
> e02 = c(-2.95,3.91,16.00,22.21,25.78)
> e12 = c(-2.33,4.17,16.3,24.02,29.12)
ref = c(0,7.1,13.8,20.7,28.6)
e01 = c(-3.14,3.71,15.87,21.05,25.33)
e02 = c(-2.95,3.91,16.00,22.21,25.78)
e12 = c(-2.33,4.17,16.3,24.02,29.12)
matplot(ref,cbind(e01,e02,e12),xlim=c(-5,30),ylim=c(-5,30))
abline(h=0,v=0)
abline(0,1)