A new method is described for computing the reciprocal of time for use in reaction rate methods. The instrument is all-electronic and can be used to measure the rates of both fast and slow reactions. The computer can be directly calibrated in reciprocal time or concentration units. Results are presented for synthetic signals which vary in rate from 5 mV/sec to 20 V/sec. Standard deviations and relative errors are less than 1% in most cases. Data for the determination of phosphate by a spectrophotometric rate method are presented to demonstrate the application of the reciprocal time computer to routine analysis. © 1969, American Chemical Society. All rights reserved.