Building Excel Worksheet - create a summary report.

**Purpose:**
To create a summary report based on monthly exported data, analyzing the dates and types of appointments for customers.

**Data Source Columns:**
- **Column D**: `start_at` (Date & Time)
- **Column E**: `service_names` (Type of appointment)
- **Column G**: `customer_name`

**Appointment Types:**
- **Application (Applikation)**:
- Examples:
- Haarsystem Erstapplikation
- Applikation & Umformung
- **Refit**:
- Examples:
- Seiten färben, Refit
- Refit, Seiten färben

**Analysis Requirements:**
**Output Sheet:** Create a new sheet named "Summary".

**Summary Table Layout:**

| A1 | B1 | C1 | D1 | E1 | F1 | G1 |
|----|----|----|----|----|----|----|
| Date of first Application | Total number of Applications until today | Total number of Refits until today | Average days between Applications | Average days between Refits | Average days between Applications (Aug 2024 - Feb 2025) | Average days between Refits (Aug 2024 - Feb 2025) |

### Step-by-Step Guide:

1. **Prepare the Data Sheet:**
- Ensure that the raw data is in a single sheet with the relevant columns: `start_at` in Column D, `service_names` in Column E, and `customer_name` in Column G.
The sheet should be designed to allow new data to be appended below existing entries each month.

2. **Set Up the Summary Sheet:**
- Create a new sheet named "Summary".
- In the "Summary" sheet, set up the table with the headers in the specified cells:
- A1: "Date of first Application"
- B1: "Total number of Applications until today"
- C1: "Total number of Refits until today"
- D1: "Average days between Applications"
- E1: "Average days between Refits"
- F1: "Average days between Applications (Aug 2024 - Feb 2025)"
- G1: "Average days between Refits (Aug 2024 - Feb 2025)"

3. **Calculate the Date of First Application (A1):**
- Filter the data to find the earliest date for the appointment types "Haarsystem Erstapplikation" or "Applikation & Umformung".
- Place the earliest date in cell A1 of the "Summary" sheet.

4. **Calculate Total Number of Applications (B1):**
- Count the total number of all Applications entries in Column E.
- Place the total count in cell B1 of the "Summary" sheet.

5. **Calculate Total Number of Refits (C1):**
- Count the total number of all Refits entries in Column E.
- Place the total count in cell C1 of the "Summary" sheet.

6. **Calculate Average Days Between Applications (D1):**
- Extract dates for all Applications entries.
- Calculate the days between consecutive application dates.
- Compute the average of these intervals.
- Place the average in cell D1 of the "Summary" sheet.

7. **Calculate Average Days Between Refits (E1):**
- Extract dates for all Refits entries.
- Calculate the days between consecutive refit dates.
- Compute the average of these intervals.
- Place the average in cell E1 of the "Summary" sheet.

8. **Calculate Average Days Between Applications (Aug 2024 - Feb 2025) (F1):**
- Filter the application dates to include only those between August 2024 and February 2025.
- Calculate the days between these filtered application dates.
- Compute the average of these intervals.
- Place the average in cell F1 of the "Summary" sheet.

9. **Calculate Average Days Between Refits (Aug 2024 - Feb 2025) (G1):**
- Filter the refit dates to include only those between August 2024 and February 2025.
- Calculate the days between these filtered refit dates.
- Compute the average of these intervals.
- Place the average in cell G1 of the "Summary" sheet.

### Additional Notes:

- Ensure date formats are consistent across columns to avoid calculation errors.
- Use helper columns for intermediate calculations where necessary, especially for date differences.
- Verify calculations with sample data to ensure accuracy.
- Consider using Excel functions such as `MINIFS`, `COUNTIFS`, `AVERAGEIFS`, and others as appropriate.

Once the summary table is complete, save the Excel file and deliver it. If any additional details or adjustments are needed, please feel free to reach out.