Discrepancy in used disc space

Hi all. Using Yosemite Preview 3. I'm looking at available disc space on my main (internal) hard drive. ForkLift says 377Gb free, Finder says 412Gb free. But I think Finder is lying because I tried to do a Time Machine backup to a 100Gb external drive and it wouldn't run because it needed 120Gb to do the backup (my MBP drive is 500Gb).

Anyone have any ideas? I've done a Verify partition from within Disk Utility and it came back clean, no issues found.

Weaselboy said:

That is because of hidden space used by Time Machines local snapshots and is normal. The space used for this is accounted for in Disk Util (and ForkLift apparently), but not in Finder. If you check Disk Util it should say 377GB free.

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Yup, that appears to be the case. I guess Finder follows the paradigm of not telling you what it thinks you don't need to know about. But I consider free disc space something I do need to know about

Thanks @weaselboy!