25.4 / DP = Module
25.4 / Module = DP
Convert your module sizes to DP before using the DP gear function.
Be aware this creates a "standard" gear and there is no ability to oversize/undersize a gear to fit a set centre distance. Which is often done.
A gearset may have a default centre distance of 198.83mm due to the desired ratio but the gearbox will be machined at a "nominal" 200mm centres. In most cases, the smaller gear will be oversized to get the correct mesh. It will have a fatter tooth which will increase its lifespan, being the faster turning gear, it will take more wear.