In the design, development and manufacture of digital circuitry, it becomes necessary to examine the characteristics of the devices that make up that circuitry, i.e., integrated circuits (ICs). Specifically, in the design and development of dynamic computer memory systems, high level standardization and characterization of dynamic MOS random access memories (RAMs), usually the heart of a dynamic computer memory system, must be maintained. An important characteristic of dynamic RAMs, in which the design engineer is interested, is its data retention time or maximum refresh rate. The maximum refresh rate is defined as the maximum time period between refresh cycles during which all locations in that dynamic RAM can maintain their validity. This characteristic is dependent upon a specified set of environmental conditions, and its response to these conditions must be carefully considered for the specific application. At the present time there is no convenient apparatus available for testing memories to determine maximum refresh rate. The present invention satisfies this need. The invention also provides a simple system for generating signals at progressively wider, controllable time intervals.