Boil eggs hard for 10 minutes. Halve the kohlrabi, peel, wash and cut into slices. Blanch in little boiling salted water for about 5 minutes. Drain, quench cold briefly and let drain.
Clean and wash watercress and radishes. (Leave a little green by the radishes if you wish). Cut the radishes into slices. Drain eggs, quench cold, peel and dice.
Mix vinegar, 1 tablespoon of water, salt and pepper, add oil. Loosely mix the prepared salad vegetables, sprinkle egg cubes over them and pour marinade over everything.