I have an extra seat with no rails. I would like to know if it's a passenger or drivers seat. I think they tilt in a particular way, can I set it on a level surface and tell the orientation without the slider attached? Thanks Mike Kelly

Yes. Level surface. The higher side of the headrest goes in the center of the car. So if the higher side (from the back) is on the right, it’s a driver side. Also, many driver side seats have a noticible indentation for the e-brake.

Thanks Mark, l’ll give it a look. Mike

The steering wheel is in front of the drivers seat?

In most cars, except when my wife is a passenger.

Also look for the indentation on the left side of the driver's seat for the ebrake clearance.

Pretty sure you have that backwards.

From
The back of the car looking through the rear window towards the front of the car, the drivers seat head test will be larger on the LEFT side of the seat.

The arc of the rear window of the car is such that the lower parts of the arc are at the left and right edges of the rear window. The highest part in the center of the rear window. To compensate for this the back of the headrest is thicker towards the left or right of the driver or passenger seat, respectively.

If you put both seats on level ground, the seats will be as I described. The rear window doesn’t change how you place the seats.