Many thanks for these replies. The two values were calculated, not input manually.

Yes you are correct I added a poll by mistake - this was my first attempt at a post, so got it wrong.

When I went into this forum today my post was under excel programming, so maybe the website changes things for you?

Is there any way of getting round the floating point arithmetic? I only have one digit after the decimal point so I could split the number into two cells and do two calculations and then put the numbers back together again. This would be very messy, so if anyone knows how to make sure the floating point arithmetic is correct, please let me know.