As I was about to commence the turn onto the crosswind leg, I spotted the helicopter that was supposedly joining downwind for the right hand helicopter circuit about a mile away in our 11 o’clock, at the same altitude and heading to pass just behind us, i.e., it was right in the middle of the fixed-wing circuit! If I made the turn, I estimated we would have passed within 300m of each other, so I elected to extend upwind and turn crosswind a short while later. At the time the sun was in my 5 o’clock, and I estimated that I was ‘enjoying’ the forecast visibility of 5-7 KM, however, I knew that I was cutting my own flight short. I’d estimate the visibility into sun was probably about 1-2 KM – even from only 1500’ it was barely hard to see any landmarks towards the sun. My suspicion is that the helicopter pilot never saw my aircraft despite stoves, navigation lights and landing lights, and quite possibly they never even know they had passed through an active fixed-wing circuit. The visibility reported by ATC is measured horizontally in all directions by an n observer on the ground. In conditions of low level haze, the flight visibility, measured forward of an aircraft in flight and the air-ground (slant) visibility may be significantly less than that reported by ATC. Also, the flight visibility into sun, particularly at low sun angles, will often be much reduced. The effect of haze on visibility should be covered in basic flight training.4.The ATC forecast visibility may be （ ）