How do I add real time RPM to Garmin 1040 edge? ( Speed and Cadence sensors installed)

Hi All. I have searched everywhere for this to no avail. Yes  I have a Cadence and Speed Sensor on my bike both Garmin.

I want to see my RPM, eg If im in a low gear I will maintain a certain RPM, if I move up the gears I want to keep the RPM going even though im either peddling easier or harder.

I've tried to add Data Fields in the 1040, but none are RPM. However I see RPM data at the end of the ride and it is displayed like the speed graph for each minute, but I cant find where I can have it as a data field on my screen like I have Speed showing.

Any help would be great!!

In case anyone asks, no I do not have a power meter and I dont intend to buy one.