Indoor Bike Trainer

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I don't know much about these, but I recently brought one second hand. I would like to attach a speedometer/cadence device to the back wheel, but have no idea what I'm looking at. Can anyone offer some advice please? I don't want to spend a much money, at a push I could go to £40.
Thanks in advance.

ColinTat

You don't need anything special.  I don't personally know, but this article has some simple bike computer recommendations.  The guys in the comments say the B'Twin is a good option:

https://road.cc/content/buyers-guide/11-best-cheap-cycle-computers-200543