from Astro.com:

The state of Illinois had a law which required, up to 1 July 1959, that all birth times had the be registered with CST (Central Standard Time), even during periods when daylight saving time was in force.

AC has implemented this. Thanks to astro.com for sharing this information.

Sometimes the Time Zone database used by AC may give an incorrect time zone. Why? Data in the AC time zone database prior to 1950-1960 can sometimes be incorrect or disputed. There are many reasons for this. Please use the web to search information on this.

You may know the actual time zone – local knowledge can trump the database. The database may not have been updated with this particular time zone value. Errors occur. An incorrect time zone may give an incorrect ASC and/or MC. The daylight saving change-over date may be disputed.

Note that most charts from the ‘60’s onwards will be correct as time zones were recorded more accurately during and after this era especially in the Anglosphere and Europe.

How to use:

This procedure will only be necessary on rare occasions – hopefully. In most cases AC calculates the correct time zone for your charts automatically.

Go the Edit Chart screen. Or New Chart.

Ensure that the correct local time has been entered.

Long-press over the Time of Birth field:

Time Zone Fix

Tap the Zone Abbrev. button and tap the required Zone Abbreviation from the resultant table – you may need to scroll quite a bit. For instance, the chart may require a zone abbreviation of CST.

Tap the Hours Mins. button and select the required hours and minutes from the resultant table. Note that it is possible to select a negative hour and minute. For instance, the correct Time Zone might be -06:00:00

Tap the Save button. Inspect the chart to see if the chart is now correct.

One corrected, transits and progressions will use this correct time zone.

Horary charts using the current date and time ie Now are invariably correct.

The best way to check if a chart is correct (if you need to)

Astro.com has the most comprehensive time zone database and using their free on-line chart calculation a good way to ensure that a chart is correct – they specifically allow this. AC’s time zone database is comprehensive and safe to use in most cases but the astro.com database is better.

Note that any time zone database is error prone and there is no guarantee that the resultant chart is correct especially if the chart is using a time and date in wartime or prior to the 1960’s or a country with a difficult history of recording time zone changes. Time zones from the USA, UK, and Europe tend to be more accurate.