Tractor Repair: Ford NAA draft control positioning, ford naa, draft control

Question
Hi guy... I'm new to the Tractor owner situation.
Have a question as to the selected position of the "draft control" lever.
I have a Ford 600 series 640.Lever under the seat right side.

I understand the intended function of this draft control.
I need to be more familiar with the positions of the selector and what the position represents.

 My mind has it,that in the up position,the draft control is eliminated (off)?
In the down Horizontal position,the draft control is engaged.?
 It's the in between area of these two positions,that I ask about.

 Is there supposed to be a in between?
Such as a percentage of draft control.

 Or is it simply full (up) no draft control,and (down) representing draft control?
 With a middle area not supposed to be intended functional?

 Not that I expect any tractor of this age to behave in all areas as if it were new.

I'm just trying to get the low down on how the draft control lever is supposed to be used.

I doubt I will ever require a draft control function.

 Reading (Googling) today I have an understanding of the lever being up,no draft control,down draft control...

Sounds simple.
However before the day ended,I've seen wording indicating that an in between position of the draft control lever would give an in between draft control function....

Such as(partial)draft control,based on sensitivity adjustment.
Is this correct or no??

 Or at least,an answer based on my aged 640.

 My draft control lever will not stay up. There is no tension
 on the lever that will keep it there.It falls back to the down (horiz) position.
In any case I'm just wanting to know about the intended lever
positions.
On/Off..... Or On/Off,and in between.
 Sorry for being so lengthy.....

Answer
Hello,

  It is not really intended to be an on/off lever.  It is a draft sensitivity adjustment.  The draft control is supposed to automatically adjust the height of the hitch to maintain a uniform tilling depth when pulling a plow or other implement over uneven ground or changing soil conditions.  The draft lever can be set to whatever position works best for your soil conditions and implement.  If it's not sensitive enough, it won't adjust the height enough.  If it's too sensitive, it will over-correct and adjust the height too much.  There should be a friction device on the lever shaft to hold the lever in the desired position.  Sounds like it is worn out or needs to be tightened up until it holds.