Working through the ITG training guide, I've noticed that in chapter 6 the slabs relate not to the floor they are on but the floor over, e.g. the ground floor level is set at 0.00, but the slab with its top at 0.00 relates to the basement level as its home story; the slab that relates to the ground level as its home story instead is above with its top level at 3.60.
Is this just an (obvious) mistake, or is there some logic here I'm missing? I would have though always that a floor slab for a floor would match the floor level not be above it at ceiling level?