# The API behind the nine charting steps (/en/docs/guide/guides/step-api)

Which public function corresponds to each of the nine charting steps, and which steps the configuration switches change.



*For: developers*

**Every one** of the [nine charting steps](/en/docs/guide/concepts/how-it-works) has a corresponding
public function in x-iztro. Everyday charting never needs them — call the charting entry point
instead. This page serves two needs: checking the derivation of one step, or reusing part of the
chain in a pipeline of your own.

The examples below use the chart for 2000-8-16, Yin hour, female — the same one as on
[How charting works](/en/docs/guide/concepts/how-it-works).

## Step-to-API mapping [#step-to-api-mapping]

### 2. Fix the month index [#2-fix-the-month-index]

```python
# 17th day of the 7th lunar month, not a leap month, Yin hour, leap correction on
utils.fix_lunar_month_index(7, 17, False, 2, True)
```

```text
6
```

[Rust](/en/docs/rust/util#fix_lunar_month_index--fix_lunar_day_index) ·
[Python](/en/docs/python/util#fix_lunar_month_index--fix_lunar_day_index) ·
[Go](/en/docs/go/util#fixlunarmonthindex--fixlunardayindex)

### 3. Locate the Soul and Body palaces [#3-locate-the-soul-and-body-palaces]

```python
utils.get_soul_and_body(6, 2, "gengHeavenly")   # month index, hour index, year stem
```

```text
SoulAndBody(soul_index=4, body_index=8, heavenly_stem_of_soul='renHeavenly', earthly_branch_of_soul='wuEarthly')
```

[Rust](/en/docs/rust/util#get_soul_and_body) ·
[Python](/en/docs/python/util#get_soul_and_body) ·
[Go](/en/docs/go/util#getsoulandbody)

### 4. Determine the Five Elements class [#4-determine-the-five-elements-class]

```python
utils.get_five_elements_class("renHeavenly", "wuEarthly")   # Soul palace stem, Soul palace branch
```

```text
wood3rd
```

[Rust](/en/docs/rust/util#get_five_elements_class) ·
[Python](/en/docs/python/util#get_five_elements_class) ·
[Go](/en/docs/go/util#getfiveelementsclass)

### 5. Place Ziwei and Tianfu [#5-place-ziwei-and-tianfu]

```python
star.get_start_index("2000-8-16", 2, "female")
```

```text
StartIndex(ziwei_index=4, tianfu_index=8)
```

[Rust](/en/docs/rust/star#get_start_index) ·
[Python](/en/docs/python/star#get_start_index) ·
[Go](/en/docs/go/star#getstartindex)

### 6 and 7. Place major stars, minor stars and adjective stars [#6-and-7-place-major-stars-minor-stars-and-adjective-stars]

Each of the three groups has an entry point returning that group's distribution across the twelve
palaces. There are also per-group slot-index functions (`get_lu_yang_tuo_ma_index`,
`get_chang_qu_index` and so on); the full list is on each language's star-placement page.

[Rust](/en/docs/rust/star) · [Python](/en/docs/python/star) · [Go](/en/docs/go/star)

### 8. Place the four groups of twelve gods [#8-place-the-four-groups-of-twelve-gods]

`get_changsheng12`, `get_boshi12` and `get_yearly12`, plus the two origin functions
`get_changsheng12_start_index` and `get_jiangqian12_start_index`.

### 9. Derive decadals and age fortune [#9-derive-decadals-and-age-fortune]

```python
r = utils.get_decadals_and_ages(4, "wood3rd", "female", "gengHeavenly", "chenEarthly")
print(r.decadals[0], r.ages[0])
```

```text
Decadal(range=(43, 52), heavenly_stem='戊', heavenly_stem_key='wuHeavenly', earthly_branch='寅', earthly_branch_key='yinEarthly') [9, 21, 33, 45, 57, 69, 81, 93, 105, 117]
```

<Callout title="Reading the output">
  This low-level function takes no chart language, so the display fields come out in the default
  Simplified Chinese: `戊` is the stem wu and `寅` is the branch yin. The `*_key` fields alongside them
  (`wuHeavenly`, `yinEarthly`) are language-independent — predicate on those. The `ages` list holds
  nominal ages (虚岁, the reckoning that starts at 1 on the day of birth).
</Callout>

<Callout>
  This function takes a Soul palace index and a Five Elements class directly, so you do not have to
  assemble a full set of birth data first; its capability is a superset of iztro's counterpart. See
  [Migrating from iztro: API mapping](/en/docs/guide/about/iztro-parity#decadals-and-age-fortune).
</Callout>

[Rust](/en/docs/rust/util#get_decadals_and_ages) ·
[Python](/en/docs/python/util#get_decadals_and_ages) ·
[Go](/en/docs/go/util#getdecadalsandages)

## Which steps the configuration changes [#which-steps-the-configuration-changes]

| Config                  | Steps affected                                                                            |
| ----------------------- | ----------------------------------------------------------------------------------------- |
| `year_divide`           | 1 (year stem and branch) → knock-on to 6, 7, 8, 9                                         |
| `horoscope_divide`      | 1 (month pillar and the year branch used by year-derived adjective stars) → knock-on to 7 |
| `day_divide`            | 1, 2 (late Zi hour attribution) → knock-on to 3, 5                                        |
| `age_divide`            | 9 (when nominal age increments)                                                           |
| `algorithm`             | 4 (Zhongzhou takes the soul star from the year branch), 7, 8 (placement of some stars)    |
| `astro_type`            | 4 onwards (the class comes from a different palace) → knock-on to 5, 6, 8, 9              |
| Custom mutagen table    | 6 (mutagen marks) and every flying-star predicate                                         |
| Custom brightness table | 6, 7 (star brightness)                                                                    |

Per-item notes are on [Config in depth](/en/docs/guide/guides/config).