Don Lancaster designed many versions of "Decimal Counting Units" that were published in Popular Electronics and Radio Electronics. Here is an early version from 1969 that used 10 incandescent bulbs. These DCU were used to construct stopwatches, counters, voltmeters and many other projects.
SWTPC sold these DCU and many complete projects. A later versions used Nixie tubes and 7 segment LEDs. In the November 1972 issue of Radio Electronics the "Digital Grinchwal" was introduced. It had a single IC that drove 4 digits of LEDs. Later the design was released by SWTPC as the Universal Digital Instrument family.
Do you remember the SWTPC Universal Digital Instrument? It had a mainframe with a digital display and then an interface to plug in a multitude of specific instruments that used the power and the display out of the mainframe. There was a frequency counter, a time interval generator, a capacitor meter, digital multimeter, and a time base (I have this one still unbuilt).
Alan J. Parrish