# Rostopic Hz inaccurate?

Hello everyone.

Sometimes when I measure the frequency of messages in a topic, the numbers printed don't make sense.

For example:

```
rostopic hz /robot/head/head_state
```

gives:

```
subscribed to [/robot/head/head_state]
average rate: 100.000
min: 0.007s max: 0.015s std dev: 0.00097s window: 96
average rate: 100.000
min: 0.004s max: 0.016s std dev: 0.00111s window: 192
average rate: 100.000
min: 0.004s max: 0.016s std dev: 0.00100s window: 289
average rate: 100.000
min: 0.004s max: 0.016s std dev: 0.00112s window: 386
average rate: 100.000
min: 0.004s max: 0.016s std dev: 0.00105s window: 483
average rate: 100.000
min: 0.004s max: 0.017s std dev: 0.00109s window: 581
average rate: 100.000
min: 0.004s max: 0.017s std dev: 0.00116s window: 678
average rate: 100.000
min: 0.004s max: 0.017s std dev: 0.00115s window: 776
```

So it measures 776 messages in 8 seconds and still tells me that the average rate is 100.000? My calculater tells me that there are 776 messages over 8 seconds -> = 97Hz. Why aren't the numbers in my terminal not corresponding with this?