Sir; Gillian Simmons' advice to the multiples to get into healthy vending in schools (Letters, June 8, p15) looks good on the surface. But the vending market is in fact complex, requires careful management across large numbers of small volume sites and, as far as schools are concerned, is unlikely to welcome the products they offer. I suggest it is much better to leave this market to a specialist operator which really understands what children and schools want and exactly how to deliver it effectively. David Berney Managing director The Green Machine Organic & Natural Food Company {{LETTERS }}