My guitarist taught me this... Pretty sweet method of Tuning in my opinion...
Heres it is: Harmonic Tuning... AkA, Tune Check
Say your tring to tune E-A-D-G
Hit open E, then on the A string (lightly touch the above the 7th fret)
If these 2 match move to...
Hit open A, then on the D string (lightly touch above the 7th fret)
If these 2 match...
Hit open D, then on the G string (lightly touch above the 7th fret)
If these 2 match, your bass is very sweetly in tune

I play a 5 string, so its the same method, just starting on the open B to the 7th fret on the E string...
I usually do this after tuning with my electric Korg tuner... Just to double check..
I learnt this pretty easy (my lead guitarist at my side tuning his guitar with a very similar method)...
if you can do it, or feel like tring... Take a few minutes and let me know how it went on here...
Take Care, and Good Luck !