Automatic feedback controllers are designed to adjust an air-knife which regulates the deposited mass in hot-dip galvanizing. They are believed to be the first controllers which correctly account for features making feedback control difficult: nonlinearity due to uncertain gain, distance-velocity lag, non-observability of some uncertain variables, interactions between the timings of distance-velocity lag, irregular gauge scanning, discrete-time feedback control, and on-line computer implementation. Simulations and preliminary full-scale trials indicate that the controllers make continuous automatic control a practical reality, thus offering substantial savings in zinc consumption.