Looking at Realtime trains at Clapham Junction I notice a sea of STPs and virtual no VARs. I always thought that STP, as the name suggests, was used for services that were added to the system at short notice due to an unexpected incident, while VAR was used for tweaks to an existing service. In the above example, most (all?) of these STPs have associated CANs. While it may not make much difference overall I wonder why it has been done like this. By contrast, services through Reading are making far more use of VARs. Just curious.