In the original operators manual for Defender, it says:
#18 - Starting Difficulty: 0=Liberal; 1=Moderate; 2=Conservative
#19 - Progressive Wave Difficulty Limit, 4-25: e.g. 5=Liberal; 10=Moderate; 15=Conservative
(The default settings are 0 and 10, for functions #18 and #19, respectively)
In...