No, you cannot use two thermometers at the same time with Natural Cycles.
A basal thermometer is highly accurate, but there can be a small difference in measurements between one thermometer and another. For example, if you’re measuring at the same time with two thermometers, one thermometer may show a 0.1°C difference from the other.
The Natural Cycles algorithm analyzes your temperature curve throughout your cycle and is looking for small temperature shifts to be able to locate where you are in your cycle. Using two thermometers can cause false temperature fluctuations, which can make it more difficult for the algorithm to analyze your cycle and detect your ovulation.
What if I need to change thermometers?
If you need to change thermometers for any reason, you should wait until the start of a new cycle to do so (until you get your next period).
If you have recently started a new cycle and would like to start using your new thermometer right away, you can instead exclude all temperatures taken with the old thermometer in the current cycle. That way, you can start measuring with the new thermometer right away and don’t have to wait until your next period begins.
The same applies if you want to switch to using the Oura Ring; we recommend making the switch at the start of a new cycle. You can read more about this here.