How to confirm level when doing maintenance?

[dearmosd]

I have been toying with the idea of changing my trans fluid. Long story short sounds easy except how to firm level when on jacks? Is there a certain place I could place a level on, use the "off road" tools on the instrument panel?

Knowing level was important with the task for refill purposes.

 

[1Mopar]

When I changed my transmission fluid, i put a bubble level on the edge of the transmission housing above the oil pan. Worked out good but servicing the transmission was a pain because of the cat and exhaust beside the oil fill plug.

 

[HSKR R/T]

I just eyeballed it in my driveway. My driveway is slanted, so had to jack up the rear, which you need to do anyways to get wheels off the ground.