## Measurements Results
### Bifilar and Octofilar Frequency Evaluation  
The frequency dependence evaluation of the CRs was done by calculating the relative difference between the measured and the calculated equivalent parallel resistance ratio of the CRs. Figure 9 shows the results for the 10:1 ratio between the RC-10k-D5e and the HADDAD1000-1201, from 300 Hz to 20 kHz. The ratio measurement results are in agreement with the computed ratio within the expanded uncertainty (k = 2.0). As seen in Figure 10, for the entire measured frequency range, the principal uncertainty components for the 10:1 ratio measurements are related to the RT error, the cable effects, the main balance resolution and the auxiliary balances of the bridge; for frequencies higher than 5 kHz, the main balance injection has a significant uncertainty contribution. The complete description of the uncertainty sources can be found in [33].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Isaohm Wire**} & \multicolumn{2}{c}{**Evanohm-S Wire**} \\ \hline
**Heat Treatment** & **Measured TC (\(\upmu\Omega/\Omega/^{\circ}\)C)** & **Heat Treatment** & **Measured TC (\(\upmu\Omega/\Omega/^{\circ}\)C)** \\ \hline No heat treatment & 4.9 & No heat treatment & 6.8 \\ \hline
5 h at 405 \({}^{\circ}\)C & \(-11.1\) & 15 h at 405 \({}^{\circ}\)C & \(-3.6\) \\ \hline
1 h at 405 \({}^{\circ}\)C & \(-3.2\) & 12 h at 405 \({}^{\circ}\)C & \(-2.2\) \\ \hline
1 h at 395 \({}^{\circ}\)C & \(-0.9\) & 5 h at 405 \({}^{\circ}\)C & 0.3 \\ \hline
1 h at 390 \({}^{\circ}\)C & \(-0.1\) & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Steps to achieve the correct heat treatment.  
Figure 8: Short term stability of the bifilar, quadrifilar, and octofilar CRs.  
Figure 11 presents the results for the 1:1 ratio between the RC-1k-D and RC-10k-D5e, and the 10:1 ratio between RC-1k-D and HADDAD1000-1201. In both measurements, a linear frequency dependence of about \(-0.16\)\(\upmu\Omega/\Omega/\)kHz was observed. This linear frequency performance is not expected in the model of CRs of any geometry. Nevertheless, this similar linear frequency behavior was found on CRs and was reported in [26; 34].  
Figure 10: Standard uncertainty components (k = 1) of the 10:1 ratio measurement between the RC-10K-D5e and the HADDAD1000-1201.  
Figure 9: Graph of the relative difference between the measured and the calculated frequency dependence of the equivalent parallel resistance of the RC 10K-D5e and the HADDAD1000-1201 10:1 ratio, as a function of frequency [24].  
Some possible causes for this behavior are the bridge with which the measurements were made, the CRs dielectric, and the terminal-wire joining. Nevertheless, the measurement system is discarded because the bridge has been previously characterized by the same CRs employed in the international EURAMET comparison and no linear frequency dependence was found [23]. The dielectric in the CRs is not the reason because all the CRs have air as dielectric and were exposed to the same environmental conditions, and the linear frequency dependence is observed only when RC-1k-D is used. The most likely reason is located in the wire or the terminal-wire connections [26], due to damage caused by a very strong blow to the CR container during transport.