Data were also evaluated based on their respective sensitivity values. Briefly, we define sensitivity as the ratio of modulation depth divided by the root-mean-square experimental noise; this modulation-to-noise ratio is further normalized as described previously, thereby allowing a direct comparison of sensitivities obtained in different studies (see SI for details on sensitivity analysis and tabulated values). Here, of particular interest was the direct sensitivity comparison to CuNTA-nitroxide ctRIDME measurements on the same GB1 construct as used in this study (GB1 I6R1/K28H/Q32H, with R1 being the name of the side chain obtained from MTSL-labelling of a cysteine residue) at 50 nM and at 100 nM protein concentration. As detailed above, the ability to excite the full width of the trityl EPR spectrum should lead to an increase in sensitivity of approximately a factor of 3 to 4 in an ideal case. Indeed, our data revealed an improvement of more than a factor 3 (Table ), and we were able to measure a 50 nM GB1 sample overnight (17 hours) instead of averaging for about 60 hours, while we would refrain from using the data obtained at lower concentrations using ctRIDME due to the poor modulation-to-noise ratios achieved. The sensitivity comparison also identifies the 25 nM sample as an outlier of the series, with an extrapolated sensitivity of around half of the expected value, while the 100, 50, and 10 nM samples are in good agreement with extrapolated values (see Table , column "St at 1 M extrapolated").