Whats a good freq to measure baseline SPL when calibrating a sub?

So I finally got my REL T/5i sub and will be calibrating it this weekend.  I have an SPL meter and a test tones CD.  I know the first step is to pick a test tone to set the baseline SPL from my monitors which I will use to compare the  low freq response of the sub.  Can someone please recommend a good starting freq?
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How about all of them, aka pink noise? Cheers,
Thank you for the reply.  I thought it was better to use specific freq test tones to set up the sub???
One more idea:

If you can generate both pink noise and white noise, sweep both. IMO, pink noise will give you better octave to octave balance while white noise will be more helpful for optimizing the hand-off from subwoofer to main speaker.
I've found that to get a REL sub right is to simply find out what your main speakers are doing…i.e. where their lows actually go (speaker specs aren't always accurate) before running out of gas, and I use a Stereophile test cd for that. I adjust my subs to start in around that frequency and…I can't make this point enough…use your ears to get them to sound like YOU want them to, which requires putting them in the part of the room that works best. Note that I still turn the level up and down here and there relative to the recording I'm listening to (I have "chicken head" knobs on the level pots on both my RELs to make this easy). Music is by far the best way to see what music sounds like…who knew?
I agree with the Wolf - Use your ears. I tried using a test cd with tone sweeps to blend in my Rel with my speakers. Once I got what sounded like a  perfect blend the bass was severely overpowering once I started playing music.