Apparatus for displaying distance reference marks on a radar screen

Claim 1

Apparatus for simultaneously producing fixed distance reference marks and an adjustable distance reference mark on the display device of a reflected beam position-finding system, comprising, in combination: pulse generator means for producing timing pulses spaced with a period equal at most to the smallest time interval which is to be adjusted; pulse counter means, connected to the output of said generator means, for counting said timing pulses and producing a digital output indicative of the count in said counter means; means for causing said pulse counter means to begin counting said timing pulses when said position-finding system transmits a beam pulse; adjustable preselector means, connected to said counter means for producing a first marking pulse each time said counter means produces a digital output indicative of a particular, preselected count; means, connected to said pulse counter means, for producing second marking pulses each time said counter means produces a digital output indicative of preset fixed counts of said timing pulses; and means connecting the outputs of said preselector means and said second marking pulses producing means to said display device for causing said display device to display a mark in response to each of said first and second marking pulses whereby the mark displayed in response to said first marking pulse is indicative of a particular adjustable preselected distance and the marks displayed in response to said second marking pulses are indicative of particular fixed distances.