The office engineer or laboratory engineer can design mixes for ultimate job design strength, but he has to provide alternatives in the design, in the form of curves and graphs. These accounts for variations in job temperature at placing time and during curing time, as well as for variations in aggregate gradation and their effect on water/cement ratio and strength. These steps make the procedures now used quite complicated to follow and to be understood by the ready mix supplier, the contractor, or the architect. The mix design job should be turned over to the field engineer for simplification of the procedure. The field engineer can eliminate many of the variables because he is familiar with the materials used. He has made or can make sieve analyses of aggregates and water/cement versus strength tests of field-made concrete cylinders, and he knows the temperatures for concrete curing. If the field engineer has all of the above responsibilities, he controls the quality of the concrete job. He is obviously far more than an inspector or technician. He must know a great deal about concrete materials and technology. He must have the authority to change the contractor's mixes and procedures if necessary. And, finally, he must be properly paid for his important job of quality control.