```python
from typing import List

import math

def mean_window(readings: List[int], sizes:    if not readings or not sizes:
        return []
    
    results = []
    for size in sizes:
        if size <= 0:
            continue
        if size > len(readings):
            results.append(0)
            continue
        
        for i in range(len(readings) - size + 1):
            window = readings[ii:i+            results.append(math.floor(sum(window) / size))
    
    return results
```