The astrologer and chart collector Lois M. Rodden introduced a categorisation of birth times, which are generally accepted among astrologers:

• AA: Accurate-accurate. Data is recorded a short time after the birth has taken place, either by the hospital staff (in a birth certificate) or by the family, e.g. in the family Bible.
• A: Accurate. Data is quoted (not read) from the chart-owner himself/herself or a person close to him/her.
• B: Biography or autobiography. There is a written source, but the birth time was written down long time after the birth took place.
• C: Caution, no source. The birth time may appear in a chart collection, but no source is given. C data is typical for historical persons like e.g. Alexander the Great, Julius Caesar or Anne Boleyn.
• DD: Dirty data. There are more than one source, and the sources are conflicting. An astrologer's sincere attempt to find the correct birth time by rectification may be dirty data. Another astrologer may reach a different result.
• X: There are no birth time, only a birth date and a birth place.
• XX: There are no birth time, and not even the birth date is reliable. Christopher Columbus could be a good example of XX data.

As an astrologer I need the birth time to be precise, because the most important events in person's life are indicated by aspects to the axes, i.e. ASC and MC, which depend on the birth time and birth date. Aspects to other factors, which only depend on the date, are less importent. Example: Transit Pluto conjunction radix ASC indicates a more important event than transit Pluto conjunction radix Sun or Moon. If the birth time is wrong, my astrological prognosis will also be wrong - by days, weeks or months - or even years.

Apart from that, we human beings tend to distort information, when we pass it on to others.

• The midwife wrote the birth time in the birth certificate one day after the birth took place. The delay was caused because she was very busy that day, and since she delivered more than one child that particular day, there is a risk of writing the wrong birth time in the birth certificate. Furthermore, after one day, she may not remember the exact time very well. Also we all know that some hospital staff members are very meticulous, while other are more sloppy.
• An astrologer looked up the birth time many years later and wrote it down for his/her own use.
• After some time the birth time was passed it on to a public database like AstroDataBank.

Each time an information is passed on, an error may happen, simply because it is human to error, and all information tend to be distorted somewhat, when it is passed on from one person to another.

Normally I need 4-5 rectification events; a portrait photo may replace information about a rectification events, because a person's appearance depends on the ASC and the dominant planets - which in both cases depend on the birth time.

A rectification event can be any event which was important in that person's life, e.g. birth of siblings or children, marriage, health crisis, death of family members or friends, career events, education - any milestone in a person's life.

For each rectification event I need to know:

• What happened? (a headline will do)
• When did it happen? (a date)
• Where did it happen? (a geographic location)

I divide my chart rectifications into 5 different categories:

• Normal
• AM-PM error
• Wild
• Speculative
• Wrong

Normal
When a chart rectification is "normal" it means that there is a given birth time, and that the rectified chart is within +/- 2 hours from the given birth time.

AM-PM error
As a software tester, I am trained to identify where the most probable errors will be made in a computer system, merely by reading the requirements for the system, i.e. even before the system has been created. When this skill is applied on rectifications, it is clear that the most probable error is when AM and PM have been switched. For example the birth time 10 AM may have become 10 PM.

Wild
It is important to be open for the possibility that the "correct" or "real" birth time is outside the scope of +/- 2 hours from the given birth time, even when the given birth time is a so-called AA information. Sometimes only a wild rectification time will match the rectification events.

Speculative
If no birth time is given, the only option for the astrologer is to make a speculative chart. Not only the rectification events shall match, the chart in itself shall also match the chart-owner's personality.

Wrong
No astrologer is perfect, and after a rectification has been made and maybe even published, you may discover after some time and with more information about the chart-owner, that the first rectification was wrong. There are cases, where I never feel completely sure that I have reached the correct rectification, even after I have been through all 24 hours of the birth date. Such a case is actress Meryl Streep, for whom I have 2 rectified charts.