 His difficulty was in producing a clock that was not affected by variations in temperature, pressure or humidity, remained accurate over long time intervals, resisted corrosion in salt air, and was able to function on board a constantly-moving ship.Many scientists, including Isaac Newton and Christiaan Huygens, doubted that such a clock could ever be built and favoured other methods for reckoning longitude, such as the method of lunar distances.Huygens ran trials using both a pendulum and a spiral balance spring clock as methods of determining longitude, with both types producing inconsistent results.