Table 2 Full factorial DOE of SAMPLE1 (300nm) showing the averaged RMSE, \(R^2\) and Thickness (nm) per combination of factors (Angle vs Height). Notes: (i) The Thorlabs PY005/M base was re-positioned when measuring RIGHT-LEFT and FRONT-BACK positions. (ii) Each data value is an average of thirty readings performed by all the sensors. (iii) *Calibration point @ height = 2mm from the sample surface.

0.5

0.0316

0.0241

0.0194

0.0176

0.6693

0.8665

0.9312

0.9416

304.55

301.13

300.6

300.76

0.33

0.0258

0.0188

0.0157

0.0171

0.8202

0.9315

0.9571

0.9433

301.46

301.58

301.11

300.47

RIGHT

0.16

0.0218

0.0141

0.0142

0.018

0.9086

0.9707

0.9643

0.9408

300.65

300.93

300.84

300.07

CENTER

0

0.0207

0.0124

0.0146

0.0197

0.927

0.9791

0.9644

0.9305

299.69

300.08

299.34

300.12

0.16

0.0204

0.0135

0.0158

0.0208

0.919

0.9732

0.9571

0.9215

299.17

298.11

298.97

299.63

0.33

0.022

0.0171

0.0179

0.0218

0.8739

0.9486

0.943

0.9116

299.55

297.82

298.94

298.64

LEFT

0.5

0.026

0.0212

0.0208

0.0225

0.788

0.9036

0.9209

0.9018

298.1

298.37

298.77

298.45

0.5

0.0271

0.0217

0.0202

0.0203

0.7751

0.9051

0.9292

0.9284

299.56

300.34

301.36

301.12

0.33

0.0236

0.018

0.0173

0.0191

0.8575

0.9409

0.9486

0.9325

300.05

299.82

300.23

300.53

BACK

0.16

0.0207

0.014

0.0154

0.0186

0.915

0.9685

0.9589

0.9357

299.38

299.79

299.74

300.08

CENTER

0

0.0189

0.0115

0.0142

0.0187

0.9434

0.9805

0.965

0.9368

298.79

299.32

299.91

300.76

0.16

0.0242

0.0127

0.0132

0.0181

0.8937

0.9776

0.9701

0.94

299.01

299.18

299.05

300.26

0.33

0.0267

0.015

0.0135

0.0174

0.8504

0.9664

0.9686

0.944

299.09

298.83

299.29

300.48

FRONT

ANGLE (\(^{\circ }\))

0.5

0.0341

0.0202

0.0157

0.0166

0.7132

0.9311

0.9616

0.9481

301.33

298.39

299.24

299.56

RMSE

R\(^2\)

Thickness (nm)