Line graph straightens itself

[Brian]

I have a list of exchange rates for a year (three different combinations of
currencies). I produced a line graph showing the three rates moving during
the year, and put the graph on a sheet of its own. I then went back to the
tab with the data, then back to the graph, and the three lines had gone
straight, as if they were trend lines, not the raw data.

Any suggestions? This has never happened to me before.

Many thanks.

 

[BrianB]

Double click the line to get :-

Format Data series/Patterns/Smooth lines may be what you want.

 

[Brian]

I thought of that, but the Smoothed Line box is NOT ticked. That's the
mysterious part of it.