Malnutrition is a leading cause of preventable deaths in infants and children. However, to benefit from treatment and prevention programmes, malnourished children must first be identified. Low weight-for-age is an anthropometric indicator of malnutrition which is gaining much recent attention because it is particularly effective at identifying children at highest risk of death. However, assessing weight-for-age can be challenging. In this project we developed and tested a novel, low-cost weight-for-age slide chart (the "MAMI" chart, named after a wider but very closely related programme of work on "Management of small, nutritionally At-risk Infants and their Mothers". We compared the performance of the new MAMI chart against two traditional methods. This was done using a cross-over diagnostic study comparing the new “MAMI” slide-chart and traditional growth charts and look-up tables. Participants were health and public health professionals working or studying in the UK. Each acted as their own control, using all three methods but in random order. Under timed conditions, they evaluated hypothetical scenarios, arranged in a random sequence. Each tool's diagnostic accuracy and response rate were compared. User preferences were also recorded. This project was initially done as a MSc Nutrition for Global Health summer project (M.Monga, summer 2022).