How to use the Corrections File
The vast majority of trades take place on the trading
system of the SIX Swiss Exchange during trading hours and so are contained in the
Preliminary Market Data files which are published each
evening after the market closes. However, some off-exchange
trades are still reported to SIX Swiss Exchange in the evening. If the
reports of these trades arrive before 22.00h, the trades are
entered into the system and so are contained in the Final
Market Data files which are published at 22.30h.
It is possible that there are still some outstanding trades
at this time and that these are reported to SIX Swiss Exchange the next day
or even later. Since it is impossible continually to go back
and regenerate the Final Market Data files, we publish this
data in the Corrections Data file. This file contains the
data relating to all off-exchange trades reported to SIX Swiss Exchange that day for previous business days.
The file contains a series of corrections, one per
line. Each line contains the symbol of the security and the
date on which the correction applies. To use the data, you
- Go to the Market Data files for the date given on
the line (TradeDate).
- Find the security in the appropriate file.
- Add the numbers in the Corrections Data file to the
corresponding numbers in the Market Data file (as defined
by the column headings).
This means that in order to apply the corrections listed in
any one Corrections Data file, you may have to visit many
Market Data files. It is also possible that many Corrections
Data files may contain data to be added to the same security
in a Market Data file for a single date.
While this may sound complicated, it should be borne in mind
that corrections are usually small and are published mainly
in the interests of historical accuracy.