@ John Eacott ... Ah, yes, the 6/18 rings a bell! Curiously, I never wore/needed specs subsequently ... although I now find reading glasses helpful on occasion.
@ melmothtw ... Well, the subject had been grinding on with trials for some years when the papers landed on my desk in about 1991. Usefully, one of my colleagues in MB had been a trial participant. No major issues had been identified during previous trials, but the Medics wanted to embark on a further 5-year trial with an even wider pool of test subjects. ACAS was of the view that this had gone on long enough, and been adequately evaluated, and at some point after my departure it was clearly signed off by the AFB. Clearly, at this remove, I can't recall any of the details of the pros and cons.