Extensive experiments under non-sitting conditions were made from time to time in order to devise some method of preventing inadvertent finger contact with the grids without interfering with any possible 'ectoplasmic' contact effect. The Veroboard strips had always been set back 1/4 inch from the table edge so that anything other than deliberate contact or Joker's aid would be unlikely to produce conductance signals. If the strips or grids had been put too far back, then sitters might inadvertently or even intentionally have applied upward force without actuating the invalidation system.
