A320 Vertical speed indicator

[Black_Dawn]

In the A320 FCOM is stated that the displayed vertical speed information is normally based on both inertial and barometric data; now what I'd like to know: what kind of data does the IRS pass to the vertical speed indicator and how does interact with barometric data.

[AerocatS2A]

Barometric lags, by using both inertial and barometric data the instrument can display near instantaneous changes.