This reports the byte rate this interface was transmitting, expressed per second rather than as a bin total. Because it's a rate rather than a cumulative total, this is the figure to compare directly against this port's negotiated line rate to see whether outbound traffic was nearing saturation, which the bin's cumulative TxBytes counter for this completed, frozen 24-hour historical bin cannot tell you by itself. For example, TxBytesPerSec reading 119000000 bytes/sec on a port provisioned for a 1 Gbps Ethernet service means the egress side of that circuit was effectively pegged at line rate.