Some tasks are difficult to combine, for example (long range) volume search takes a lot of radar resources, leaving little room for other tasks such as targeting. Combining volume search with other tasks also results either in slow search rates or in low overall quality per task. Driving parameters in radar performance is time-on-target or observation time per beam. This is why the Royal Navy selected the S1850M Long Range Radar to complement Sampson on the Type 45 destroyers. It is also a reason why the NATO Anti-Air Warfare System study (NAAWS) defined the preferred AAW system as consisting of a complementary Volume Search Radar and MFR. This gives the added advantage that the two systems can use two different radar frequencies; one being a good choice for long range search, the other a good choice for an MFR (as physics makes both tasks difficult to combine).