Generally, how the S&P 500 index performs has a knock on effect on other indices such as FTSE 100.

So the key question at the moment is how much of the big January / February fall is it going to retrace?

The index peaked at 1150.4 on 19 January, and then fell powerfully until 5 February, which saw a low of 1044.5. A fall at its maximum of 105.9 (over 9%).

It is common for powerful falls like this to retrace between a half and two thirds. And Fibonacci fans like to look at other retracement levels such as 61.8%.

With the high of Wednesday 17 February reaching 1101.0 the 50% retracement level has already been achieved (1097.4), so the next two of interest could be the 61.8% retracement (1109.9) and the two thirds level (1115.0).

One scenario now is that we see a little more upside and then the retracement peters out somewhere between 1101.0 and 1115.0, leading to further declines at least testing the low of the recent decline.

Another scenario is that we see a 100% retracement of the decline, and that old January high of 1150.4 gets tested again.

The price action over the next three or four days will provide us with clues on further developments, in particular it is important to see whether the retracement can push as high as 1115.0, or if it loses strength before then.