enquiry re onboard chimes

[myrtleman]

I'm sure this is a very stupid question to those in the know but I wonder if anyone could tell me what the onboard chimes that occur intermittently during flights signify.

I've worked out that there is one chime as the plane is about to take off and one chime as it starts its approach and two on short finals, but what are the chimes during the course of the flight for?

I've been on hundreds of flights and it's only just struck me that I've never known the reason for these bells?

Thanks,
MM