STL average latency versus latency histogram

[ChristianKnoblauch]

How is the average latency is related to the latency histogram?

Sample:
'latency': {'average': 24.0,
'histogram': {0: 14,
10: 34760168,
20: 197101091,
30: 59427711,
40: 16875361,
50: 8154571,
60: 10386280,
70: 3989660,
80: 1684491,
90: 1482486,
100: 4916878,
200: 3705691,
300: 3705095,
400: 4566288,
500: 3686509,
600: 53},

Average latency is reported as 24usec.

Calculated average latency from the histogram is 40usec.
[ sum of latency of all packets / number of all packets ]
[ (34760168 * 10usec + 197101091 * 20usec + ...) / (34760168 + 197101091 + ...)]

Any explanation how TRex calculates the average?