What specific technology was used in Robert Ling's 1973 program SHADE to simulate different shades within the matrix display?

Answer

Overstruck printer characters

Robert Ling's SHADE program relied on existing printer technology, using the technique of overstriking characters to create varied shades of gray for each element in the matrix.

What specific technology was used in Robert Ling's 1973 program SHADE to simulate different shades within the matrix display?
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