Why is ‘The Chair’ so-called?

Why is 'The Chair' so-called? One of just five ‘named’ fences on the Grand National Course, ‘The Chair’ is the penultimate fence on the first circuit of the Grand National and, along with the Water Jump, is jumped just once.
Neverthless,’The Chair’ stands 5’3″ high and is preceded by a 6′ wide ditch, making it both the highest and widest obstacle on the Grand National Course. Furthermore, the landing side is 6″ higher than the take-off side, so the fence is a spectacular, if formidable, test for horse and rider; its positioning, in front of the grandstand, is no accident.

Originally known as the ‘Monument Jump’, ‘The Chair’ took its name, quite literally, from the chair which, historically, stood on a concrete plinth alongside the fence. In the early days of steeplechasing, when races were run in heats, the chair was occupied by the so-called ‘distance judge’, whose job it was to gauge the distance between one finisher and the next. Essentially, any horse that had failed to pass the distance judge when the previous finisher crossed the winning line was declared ‘distanced’ or, in other words, beaten 40 lengths or more. Any such horse was considered a non-finisher and, hence, disqualified from participating in subsequent heats. Understandably, for safety reasons, the concrete plinth was replaced by a plastic replica in Nineties, but the original can still be seen in the Red Rum Garden at Aintree.