Taking our temperature to check health has a long tradition but the Covid pandemic brought it right to the fore, and also raised the question of its accuracy. And indeed, says Prof. Graham Machin of the National Physical Laboratory, it turns out that fever screening during the pandemic was not very effective in preventing its spread; but the difficulties are now better understood, along with ways to fix them – essential information to help us cope with whatever such challenge the future may bring. Prof. Machin is a world leader in thermometry, and his team at NPL have made numerous contributions to solving temperature measurement problems from harsh environments in aerospace and nuclear decommissioning to health care.