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An ion chamber current meter spanning seven decades from 10 fA to .1 Â¿A is described. It is based upon a current-to-width conversion technique implemented by a gated-integrator preamplifier. Performing automatic offset and bias current adjustments, it achieves a particularly long-term service-free operation. A complete analysis of its noise is made; signal-to--noise optimization is attained by means of a self--adapting filter.