Large area spark counter with fine time and position resolution

The key properties of spark counters include their capability of precision timing (at the sub 100 ps level) and of measuring the position of the charged particle to high accuracy. At SLAC a program to develop these devices for use in high energy physics experiments involving large detectors was undertaken. A spark counter of size 1.2 m x 0.1 m was constructed and has been operating continuously in a test setup for several months. Some details of its construction and its properties as a particle detector are reported.