In the blizzard of numbers published about royal finances, there is one figure that's very revealing. It's £99.9m for the level of next year's Sovereign Grant, the public funding for the running costs of the monarchy, covering costs like travel, staff and building maintenance. Not £100m, but £99.9m, the type of figure we're used to seeing in retail settings - £9.99 rather than a tenner - keeping a figure below a threshold, in a sales tactic that's sometimes called "charm pricing" or "