Perhaps the watch had some sentimental value which kept it being worn after the 'slide rule' loss. But then you'd imagine that he'd have been able to have the part replaced, assuming that they were still available by the time of the loss. Odd. Yes I'd imagine that the Calculator would appeal to your typical car designer of the time, as no doubt would the Monaco had it not become 'racer-ised' - I'm assuming that this advert dates from pre-Le Mans when it was still intended to appeal to architects, designers etc. But then the narrative seems a bit 'flamboyant' to be aimed at that demographic ?!... And getting back to the Calculator, we should mention the bracelet in the shot which looks correct for the model ?