Chop the cranberries very coarsely and place them in a small bowl. Toss them with the sugar.
Peel, core, and cut the pears into wedges. Sprinkle with the lime juice.
Line a glass salad bowl with the watercress, arrange the cranberries, pears, and pistachios over the watercress. In the bowl of a wooden spoon mix a sprinkling of salt with the vinegar, stir to dissolve with another wooden spoon, and toss over the salad. Spoon over the olive oil and grind over some pepper. Toss gently. Add salt and pepper to taste.