Nauticalia

Until now, there's been no easy way to tell how much gas is left in a bottle, so you either end up wasting money by taking it back too soon for a re-fill, or running out at an inconvenient time - cooking a meal at sea for example, or in the middle of a cold night when you could really do without changing the bottle to keep the heating going. This clever little indicator works by monitoring the temperature difference between liquid gas (which sits at the bottom) and gas in vapour, changing colour at the appropriate level. Very simple and easy to use, works for both butane and propane and all sizes of bottle (you only need to know the level when it is near the bottom).

Buy two for £15.98 and SAVE £4.