rpm on turbo trainer

What is the easiest way of knowing the rpm whilst using turbo trainer?

A cycle computer with a cadence sensor.

^ Yes,that

count
Cadence on the bike computer

Garmin GSC10 with a 200/500

Ha! I wrote ‘count’ then thought “nah, CBA to put that”, but actually, counting for 15 seconds gives a good idea.

A bike computer will work on the turbo. It also has the side effect of working off the turbo. I don’t know if this is a problem to you?

A bike computer will work on the turbo.

Only a rear wheel mounted one, although the cadence will of course work regardless.

Righto – thanks.
(tried counting but interferes with sing-a-long to Dolly Parton soundtrack)!