Previously we used the metaphor of photography in regard to astrology and said that the general natal reading was like using a wide-angled lens. Once one has got a general idea of where his life is going, he may want to zoom in on a particular time frame to get more details. This is called an "update reading."
A person's life cannot be encapsulated in a few hours. Because it is impossible to do everything in one sitting, people often have follow-up readings that cover certain time frames. People usually ask about what the next six months or one year will hold in store for them. Many people have their charts updated around the beginning of the New Year, or near their birthday, and thereby have a report for the upcoming year. One may want a chart updated because of contemplating a new business, changing his residence, having marital, legal, or health problems, etc. There are no hard-and-fast rules regarding when or why to have a chart done, or for what span of time. One's needs should be the guideline for this.
Follow-up readings are almost exclusively predictive in nature. They will reveal in greater detail the types of situations, both physically and mentally, that you one will find oneself in--times of strength or weakness, happiness and sadness, romance, love, health, illness, travel, education, etc. This type of reading is quite popular with business people, executives, and anyone (that includes you) who needs to have the best information available for decision- making and planning. These kinds of people know the value of a good advisor who can suggest strategy for progressing in material or spiritual life.
Closely related to update charts but of generally longer duration are charts that focus on a particular planetary period or sub-period. These will normally cover time frames of several years in duration. It is advisable for anyone who had such a longer forecast done to have his chart updated at least annually, if not every six months. The reason is simple: the shorter the span of time investigated, the more detail revealed.
Year Overview: this update focuses on the highlights of the coming year giving the general trends and important dates to watch out for, both good and bad. This kind of general update reading is adequate for most people.
Year Month By Month: this update includes the same information as the Year Overview but is much more detailed breaking down the year into months and giving the important dates and events of each month. This type of reading is in great demand by business people, military officers, managers, traveling sannyasis and anyone to whom knowledge of upcoming trends is mission critical.
Detailed reading of one Mahadasha: in Vedic astrology, cycles of time are broken down into planetary periods called Mahadasha. Each planet rules over one of these cycles, the length of time varies according to each of the planets. The longest is 20 years (ruled by Venus), the shortest is 6 years (ruled by the Sun). All together the aggregate of years is 120 (very few people live through the whole cycle). It is very useful to get a detailed reading of a mahadasha because it gives a more long-range view of what is in store, this is simply impossible for a yearly reading to do. Things could go very well one year and terrible the next. If you had a long-range view you could take advantage of the good year to compensate for the bad year that would follow. The cost for such a detailed reading is variable depending on the amount of detail you want. A Mahadasha is itself broken down into Bhuktis--sub-periods. So a detailed reading of a Mahadasha could include all of the sub-periods and major transits, or just a in-depth overview of the Mahadasha (without the Bhuktis). This would still would be in much greater detail than could be done in a general natal reading. People often have update readings on a Mahadasha when they are near the end of one Mahadasha and about to start a new one. A change of Mahadasha often signals major changes in life, so it is wise to know what is in store for you in the future.
Detailed reading of one Bhukti: as mentioned above a Mahadasha is divided into sub-periods; nine to be exact, one for each of the planets; these sub-periods are called Bhuktis. They are variable in length and some can be over three years in duration. There are definite life changes with the beginnings of new Bhuktis. People usually have a update reading on a Bhukti when they are about to start on a longer one (2-3 years) and need to know what is in store for them. (Usually shorter Bhuktis can sometime be included in a one-year update, or they can overlap into a second year.) The cost of the reading will depend again on the amount of detail that the seeker requires. Does he just want an overview of what is in store, or do they want to know more details such as could be seen if we also include major transits.
Detailed reading of special time span: the seeker determines what time frame is important to them--the next 3 years, 5 years, 10 years, whatever they think is important. Again, the cost of the reading will depend on the length of time covered and how much detail they require--do they just want an overview or a detailed analysis.