LONDON -- The FTSE 100 (INDEX: ^FTSE) has been up and down 20 points or so today, and currently sits on 5,771 points, just five points down on the day, as there appears to be weakened interest in the markets ahead of expected updates from central banks.

But whatever the index aggregate is or isn't doing, individual shares are still moving up and down every day. We look at three members of the various FTSE indexes whose shares are sliding today...

Chemring
Chemring (LSE: CHG.L) saw its shares crushed today, down 46.5 pence (12.6%) to 324 pence, after the manufacturer of air defense countermeasures released a profit warning.

Although business in the three months to July 2012 saw steady growth, the firm told us that it has discovered errors in a new Enterprise Resource Planning system being installed at its Florida subsidiary, and that there are delays to the start of production of one of its new products. Together, these are expected to knock 15 million pounds, or the equivalent of around 6 pence per share, off full-year operating profit.

G4S
Interim results from security firm G4S (LSE: GFS.L) confirmed a minimum 50 million pound price tag for its Olympics contract debacle, and that helped push the price down 6.4 pence (2.4%) to 260 pence. And the 50 million pounds might not be the end of it, as the final costs are not all in yet.

Pre-tax profit for the period slumped 60% as a result, to 61 million pounds, even though revenue rose by 5.8% to 3.9 billion pounds. We also heard of a 24 million pound charge and the loss of more than 1,000 jobs as part of the firm's restructuring plan. But the biggest worry now has to be of longer-term damage to the company's reputation, and we won't really know the extent of that for some time.

Lamprell
Lamprell (LSE: LAM.L), the provider of engineering services to the oil and gas industry, suffered a modest fall of 1.1% to 89 pence on the release of interim figures, which showed a net loss of $47.1 million, down from a profit of $18.6 million at the same stage last year.

The six-month period, which saw the share plunge by around 70%, was plagued by a series of contract delays and led to a series of profit warnings. The firm told us its order book is healthy, its financial position is secure, and that it is implementing changes across the company -- but it may take investors some time to be confident there are no more shocks to come.

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