When last I looked there were more down shares than up today, yet the alsh is up 0,43%. Most of this is due to NPN. Thus the level of the alsh is not necessarily a true reflection of what's actually happening.
The top 6 shares in the ALSI make up a market cap of ZAR4.3tn - (excluding SAB and Annauser Busch, which i understand no longer participate in the top40). All of these are ZAR hedged foreign traded stocks. The remaining 34 shares make up another ZAR 4tn. So you can see how important currency moves are to our index.