The equipment as designed and constructed is a workable solution to the problem of mixing air and oxygen at selectable oxygen concentrations and flow rates. Control of the flow of the individual gases is adequate with the metering elements as designed. The laminated brass stock and shim stock is easily fabricated and works well. The mechanical linkage is the weakest link in the design. The hysteresis in setting concentration and the inaccuracies in setting concentration are primarily related to poor design in the linkage. Ways to possibly improve the linkage are discussed in the Recommendation section of this thesis. The only problem with the read-out design is at low flow rates, i. e., less than 5000 cm³/min (5 -(min)) the scale sticks at times. / Master of Science