LONDON -- The FTSE 100 (FTSEINDICES:^FTSE) is continuing the down day it had last Friday, dropping 19 points to 5,903 as of 10:15 a.m. EST. Still, it's only a small fall, and the index of top U.K. stocks did reach new nine-month highs several times last week.

Some individual constituents of the various FTSE indexes have experienced somewhat bigger falls today. Here are three on the way down:

Aggreko (LSE:AGK)
The Aggreko share slump continued today as the price dropped a further 20% on the release of a pre-close trading update. Expectations for 2012 actually sound pretty good, with full-year performance said to be in line with expectations and earnings per share rising by "at least 15%."

However, the company, which provides temporary power supply and temperature-control equipment, also warned that 2013's performance is likely to be below this year's, suggesting that turnover would be down about 100 million pounds, with EPS no better than flat, whereas previous forecasts has suggested a 10% EPS rise.

Hunting (LSE:HTG)
Hunting, the oil and gas services group, saw its shares fall 5.5% on the release of its pre-close trading statement, even though things look pretty reasonable. Trading is in line with expectations, net debt is modest at 205 million pounds, and the firm has resolved a tax dispute in its favor.

But the usual bugbear is Hunting's outlook: The firm said "the short term outlook is increasingly cautious due to the economic climate seen in a number of our operating regions."

Vodafone (LSE:VOD) (NASDAQ:VOD)
Shares in Vodafone have dipped 1.9% to 158 pence after the telecom operator announced the latest purchase in its share buyback program. Six million shares have been purchased at a price of 161.7 pence per share, taking the total purchased since Dec. 10 to 33 million for a total cost of 53 million pounds.

Share buybacks are supposed to boost shareholder value, but it's a controversial subject. And Vodafone's recent share-price slide has not been a testament to success in this instance. But who can resist that 7% dividend yield forecast for the year to March 2013?

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Alan does not own any shares mentioned in this article. Motley Fool newsletter services have recommended buying shares of Vodafone Group. The Motley Fool has a disclosure policy. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. Try any of our Foolish newsletter services free for 30 days.