When it comes to test instruments for current measurements, you should always be able to find information about how accurate the measurements will be. You will find this in the terms of ±(gain error + offset error), ±(X% + Y), which means that your measurement value can be offset by an error of Y and have a percentual error X.
The accuracy for the main channel for low currents of Otii Arc is ±(0.1% +50nA). So, what does that mean when it comes to the real measurements? How does this affect the measurement accuracy? Let us compare the Otii Arc accuracy with another measurement instrument with a quite common accuracy of ±(1% +1uA).
Here is one example:
Let say you want to measure a sleep current of 1uA.
When measuring with Otii Arc you can get following result 1uA± 51nA (0.1% of 1uA is 1nA and then add 50nA = 51nA). If you use the other measurement instrument then the measurement can show 1uA ± 1uA (1% of 1uA is 10nA and then add 1uA = 1010nA). If you want an accurate measurement of the sleep current of 1uA and you measure between 0uA to 2uA it is obvious that this is not very useful.
Perhaps the best way to highlight this is to set up a table showing the absolute error (uA) together with the percentage error for different current measurements.
Having this in mind will help you pick the right tool for your development project and avoid yet another pitfall in getting that low current consumption of your device.
For more current ranges for Otii Arc, check out the tech spec.