```python
def mean_window(readings: list, size: int) -> list:
    if size <= 0:
        raise ValueError("Window size must be greater than zero")
    
    results = []
    for i in range(len(readings) - size + 1):
        window = readings[i:i+size]
        result = sum(window) // size
        results.append(result)
    
    return results
```