Lastolite XpoBalance 38cm (15")  Ref: 1558
Angela Nicholson, writing in Amateur Photographer 25.3.06 said....
"Grey Cards have been available for many years to help photographers select the correct exposure settings when using a TTL metering system, but Lastolite have taken things a step further with the introduction of the XpoBalance.
This triangular device has white, mid-grey and black segments on one side and light, mid and dark grey segments (plus or minus half EV) on the other. While the mid grey sections can be used to set exposure, the side with black white and grey allows the digital photographer to produce a balanced histogram. This is simply a case of filling the frame with equal amounts of each tone and adjusting the exposure until the histogram (live or recorded) shows three fairly equal peaks. The midtone peak should be centred with no loss of the black and white peaks at opposite ends. Once you have found the exposure settings that achieve this, your image should contain the maximum possible level of detail in both the shadows and the highlights. It's simple, but effective."