I have a 2 TB volume presented to vSphere and don't understand what the reported compression rate really means

According the the GUI, the compression factor is "This value is the compression factor of the volume (including snapshots).

Compression factor = Pre-compressed space / Post-compressed space."

So - the pre-compressed space is what vSphere reports as used ?

post-compressed space is what the Nimble GUI shows as primary used + snapshot used?

if so, then the compression rate should be 1.62 TB / 630 GB which yields ~ 2.7 but the Nimble GUI show 1.31 as the compression factor.

Obviously, I'm missing something here.

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I have a 2 TB volume presented to vSphere 5.1

Virtual Center shows

Capacity : 2 TB

Privisioned Space : 1.62 TB

Free Space : 384 Gb

Nimble GUI shows

Volume Space

Size 2.0 TB

Used 246 GB

Reserve 0

Quota 2.0 TB

Primary Compression 1.31 X

Primary Space Saved 76 Gb

Snapshot Sapce

Used 386 GB

Reserve 409 GB

Quota Unlimited

Backup Compression 1.29x

[EDIT] my previous response to David was incorrect - thanks to my colleagues @ Nimble for educating me on the math

calculation for space saving should be:

1.31X compression is 1 - (1/1.31) = .24 or 24% savings

2.x compression = 1 - (1/2.0) = 0.5 or 50% savings