Thank you Randy.
I had tried Amazon but not found a filter which fitted my 24" screen; but you have!
I shall be very pleased provided that the filter works and that I can adjust the refresh rate and screen brightness. I'll find out when the filter arrives.
The screen has now arrived. I hope it will help my eyestrain, although I don't know if the flicker is reduced. The screen was tricky to fit.
The main problem is that the screen is widescreen and as you will know my monitor is not. So I've had to cut off a strip of the side and am left with a gap top and bottom. Not deadly but a pity.