Retractable stair system with precision elevation control

A retractable stair system for a vehicle, comprising:

• a frame, said frame comprising a first side plate having a top and an inner side, and a second side plate having a top and an inner side, said first and second side plates located at a first frame side and at a second frame side, respectively, and spaced apart by longitudinal structural members, said first side plate and said second side plate each further including (a) first edgewalls defining an annular arc slide guide cutout therein, and (b) second edgewalls defining a recessed latch finger cutout therein;
• a first keeper plate and a second keeper plate, said first keeper plate and said second keeper plate pivotally affixed to said frame at said first frame side and at second frame side, respectively;
• a first indexing plate and a second indexing plate, said first indexing plate and said second indexing plate pivotally affixed to said frame at a first frame side and at a second frame side, respectively, and each of said first indexing plate and said second indexing plate further comprising an arcuate upper surface having a plurality of locking notches downwardly recessed therein;
• a first latch and a second latch, said first latch and said second latch each having a pivot neck, and pivotally affixed at said pivot neck to said frame at said first frame side and at said second frame side, respectively, and each of said first latch and said second latch comprising a downwardly extending latch tongue sized and shaped for interfitting locking engagement with said locking notches in said first indexing plate and said second indexing plate, respectively;
• means for an extensible-retractable scissors stair assembly, said extensible-retractable scissors stair assembly comprising a first scissors assembly and a second scissors assembly, and wherein each of said first scissors assembly and said second scissors assembly comprises a plurality of outward elements and a plurality of downward elements, and wherein said first scissors assembly and said second scissors assembly are spaced apart by a number N of stairs S in a series of stairs S1 to SN, wherein N is a positive integer between two and six inclusive, and wherein each of said stairs S is securely affixed between selected outward elements of said first scissors assembly and said second scissors assembly;
• and
• wherein adjustment of said latch tongue of said first latch and of said latch tongue of said second latch between selected locking notches downwardly recessed in said first and said second index plates adjusts said stair S1 to a height HS below the top of said first side plate and below the top of said second side plate.