ADSL is a technology that has approximately 10% overhead, which essentially means that a small portion of your bandwidth is used up in the process of sending data across the network.  When comparing the speeds reported for the “sync speed” versus a speed test, a difference ~ 10% will always be present because of this.

DSL is a “best effort” but we will have accounted for this 10% difference.  For example, this would mean that for a 10Mbps service, we would provision the service at 11Mbps to make up for that difference.