## 3 Results  
An example of a measured strain distribution is illustrated in Figure 4 for the 30% deformation stage. The measurement accuracy results for all deformation stages are presented in Table 4, which indicates that the measured mean was very close to the calibrated mean for each deformation stage,  
Figure 3: (**a**) Camera set-up and (**b**) measurement locations across the calibrated volume.  
with similar standard deviation values. The \(p\)-values from the A-D tests (Table 4) show that the null hypothesis was accepted for all deformation stages, meaning the errors measured for each stage could be assumed to be normally distributed.  
In a normal distribution, 95% of the deformation error measurements at each stage should fall within two standard deviations of the mean. Using this theory, the system measurement accuracy was calculated and the results are shown in Table 5. The results for the measurement accuracy are relatively consistent across all deformation stages, with the mean error being close to zero and within a \(\pm\)0.5% strain at a 95% confidence interval.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Deformation** & **Measured Mean** & **Calibrated** & **Mean Measurement** & **\(p\)-Value** \\
**Stage (\% Strain)** & **(\(\pm\)1 SD) (\% Strain)** & **Deformation (\% Strain)** & **Error (\(\pm\)1 SD) (\% Strain)** & **\(p\)-Value** \\ \hline
10 & 9.96 (\(\pm\)0.11) & 9.95 & 0.01 (\(\pm\)0.11) & 0.575 \\
20 & 20.01 (\(\pm\)0.13) & 19.96 & 0.05 (\(\pm\)0.13) & 0.069 \\
30 & 29.96 (\(\pm\)0.13) & 29.92 & 0.04 (\(\pm\)0.13) & 0.096 \\
40 & 39.93 (\(\pm\)0.15) & 39.92 & 0.01 (\(\pm\)0.15) & 0.166 \\
50 & 49.95 (\(\pm\)0.15) & 49.97 & \(-\)0.02 (\(\pm\)0.15) & 0.098 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Measurement accuracy results calculated for each deformation stage with \(p\)-value results for the Anderson–Darling statistical test for normality.  
Figure 4: An example strain measurement distribution for the 30% deformation stage with the Speckle Pattern Board (SPB) located in the centre of the measurement volume.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Deformation Stage** & **Measured Mean** & **Calibrated Mean** & **Mean Accuracy** \\
**(\% Strain)** & **(\(\pm\)2 SD) (\% Strain)** & **(\% Strain)** & **(\% Strain)** \\ \hline
0 & 0 & 0 & 0 \\
10 & 9.96 (\(\pm\)0.22) & 9.95 (\(\pm\)0.08) & 0.01 (\(\pm\)0.30) \\
20 & 20.01 (\(\pm\)0.26) & 19.96 (\(\pm\)0.08) & 0.05 (\(\pm\)0.34) \\
30 & 29.96 (\(\pm\)0.26) & 29.92 (\(\pm\)0.08) & 0.04 (\(\pm\)0.34) \\
40 & 39.93 (\(\pm\)0.30) & 39.92 (\(\pm\)0.08) & 0.01 (\(\pm\)0.38) \\
50 & 49.95 (\(\pm\)0.30) & 49.97 (\(\pm\)0.14) & \(-\)0.02 (\(\pm\)0.44) \\ \hline \hline \end{tabular}
\end{table}
Table 5: Measurement accuracy results for each deformation stage at a 95% confidence level for measured deformations and incorporating edge detection error for calibrated deformations.  
Measurement error distributions from the 50% deformation stage were used to compare measurements from nine positions within the calibrated measurement volume. The statistical analysis (Table 6) shows that for positions at the extremities of the volume, when compared with the deformation occurring at the center, the null hypothesis was not rejected and, consequently, it could be assumed that all measurements were drawn from the same distribution. These results indicate that all measurements made were comparable and, therefore, measurement accuracy was unaffected by position within the volume.