===============Axial extensometer===========================
G=50mm

Call:
lm(formula = Pcal ~ Pext, data = cal)

Residuals:
       Min        1Q    Median        3Q       Max
-0.411607  0.002852  0.020279  0.035568  0.113338

Coefficients:
             Estimate Std. Error t value Pr(>|t|)
(Intercept)  7.80229    0.04340   179.8   <2e-16 ***
Pext         2.45417    0.02186   112.3   <2e-16 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 0.1232 on 13 degrees of freedom
Multiple R-squared: 0.999,      Adjusted R-squared: 0.9989
F-statistic: 1.26e+04 on 1 and 13 DF,  p-value: < 2.2e-16


so

displacement = (2.45417 mm/V) * Voltage

but remember that it doesn't go to zero volts at zero strain

Raw data:
Pcal : displacement in INCHES (25.4 mm/in)
Pext : extensometer voltage
Pcal    Pext
0       -3.1756
0.025   -2.918
0.05    -2.662
0.075   -2.405
0.100   -2.149
0.125   -1.892
0.150   -1.635
0.175   -1.378
0.200   -1.122
0.250   -0.608
0.300   +0.09344
0.350   0.422
0.400   0.925
0.45    1.432
0.000   -3.189

===============Axial extensometer===========================

===============diametral extensometer===========================

lm(formula = Pext ~ Pcal, data = cald)

Residuals:
       Min        1Q    Median        3Q       Max
-0.047723 -0.012053 -0.004385  0.023610  0.032941

Coefficients:
               Estimate Std. Error t value Pr(>|t|)
(Intercept) -14.809593   0.066176  -223.8 9.39e-15 ***
Pcal          1.156166   0.005317   217.5 1.15e-14 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 0.02839 on 7 degrees of freedom
Multiple R-squared: 0.9999,     Adjusted R-squared: 0.9998
F-statistic: 4.729e+04 on 1 and 7 DF,  p-value: 1.148e-14

so displacement = 1.156166 mm/V

RAw data
Pcal    Pext
0.4     -3.03
0.45    -1.571
0.5     -0.101
0.55    1.330
0.6     2.806
0.405   -2.928
0.42    -2.498
0.47    -1.055
0.57    1.946

Pcal is gage block thickness in INCHES
Pext is extensometer voltage in VOLTS

Again, zero strain does not correspond to zero volts.




===============diametral extensometer===========================