This is a numpy bug:

```
In [32]: for i in range(1, 10):
    np.set_printoptions(precision=i, suppress=True)
    print(h.center_of_mass)
   ....:     
[[-0.]
 [ 0.]
 [ 0.]]
[[-0.00]
 [ 0.00]
 [ 0.01]]
[[-0.000]
 [ 0.000]
 [ 0.012]]
[[-0.000]
 [ 0.000]
 [ 0.012]]
[[-0.000]
 [ 0.000]
 [ 0.012]]
[[-0.000000]
 [ 0.000000]
 [ 0.011997]]
[[-0.0000000]
 [ 0.0000000]
 [ 0.0119968]]
[[-0.00000000]
 [ 0.00000000]
 [ 0.01199679]]
[[-0.000000000]
 [ 0.000000000]
 [ 0.011996794]]
```