When dating fossils, it helps to be precise | Brief letters

So the fossilised jaw of a rhomaleosaur that Matthew Myerscough discovered is 201 million years old (Report, 28 July). Such precision. It reminded me of the old story of a museum guide telling a visitor that a similar exhibit was 100 million and 27 years old. When asked to justify this, he said: “When I started work here I was told that it was 100 million years old and I have been working here for 27 years.” Alan Woodley Northampton • Regarding hair washing (Letters, 26 July), I lost my shampoo en route to spending two months in South Sudan and refugee camps in north Uganda and Kenya. In the absence of shops, I just used soap to wash my hair. When I got back in the UK, I visited my hairdresser. “What have you been doing to your hair?” she asked. “I’ve never seen it in such good condition.” Maggie Hamilton Oxford • In response to Steve Penny (Letters, 24 July), it’s worth noting that George Harrison was bleating about high taxes well before the 1980s. He even wrote a song, Taxman, about it in 1966. Peter Lock Liverpool • Surely Lucy Knight was aware that Marmite on toast could only be rated 10 or zero (Letters, 29 July) and democratically awarded it the average of 5/10. Malcolm Reid Danbury, Essex • Graham Jack (Letters, 26 July) advises using washing-up water in the garden. Fine, but best not to use it on edible crops. Graham Larkbey London • Have an opinion on anything you’ve read in the Guardian today? Please email us your letter and it will be considered for publication in our letters section.