I'm not sure whether Baby B was counting his fingers here - something he likes to do quite often, just to make sure they're all still present and correct - or checking Granddad's calculations while they were going through their times tables. He seemed quite dubious about the competence of both his grandparents at various points today, so it may have been the latter.
The interesting thing about getting a weekly snapshot of a baby at this stage is that there's a step change in his abilities each time we see him. Today we noticed that when he wants something that's close to him he has no trouble at all in simply reaching out and picking it up. Putting it down again seems to be more a matter of losing interest and relaxing his grip, rather than being a conscious action, but he is already quite good at sweeping things off the tray of his high chair onto the floor. At this stage his reaction to having done this is still mild surprise, but I suspect we can't be far off it becoming an extremely amusing game.