Flyingmac,
The altimeter doesn't contain mercury. Some altimeters do have dual Kollsman scales or windows (milibars and inches of mercury). These don't mean that the altimeter contains mercury, but are measurements that reference mercury. Specifically, they reference the readings that would be obtained from a mercury barometer, or a barometer calibrated to read in "inches of mercury."
Guppy. Thanks for the explanation but my question was simply a poor attempt at what we Brits call humour.(Humor). My apologies.
I'm off now to inflate my car tyres to 75 inches of mercury.