Thanks, ladies, for your quick replies. No - I haven't looked at the chart - I've never used charts before so I didn't even think about it.
I did think of the possibility of a typo but it's repeated in other rows, so I wasn't sure. Coming back to knitting after such a long time, I wondered whether things had changed a lot.
I haven't started it yet - so thank you so much, Lilian, for saying you'll give it a go. My knitting confidence is a bit low. I've been crocheting for many, many years but my knitting is limited to hats in the round. I'm hoping the scarf will come out well and give me more confidence to try other things.
Just seen Brenda's reply too. I thought "slk2tog psso" would have to be a different instruction from the first one but the more I looked at it and thought about it, the more confused I became.
I suppose the only way to be sure is to have a go at it.