This sim­ple, yet effec­tive dip­stick gives an accu­rate indi­ca­tion of liq­uid helium depth. It is made from stain­less steel with a fine rub­ber diaphragm, held in place by an O-​Ring over the cup shaped upper end of the dipstick.

The ther­mal gra­di­ent set up in the tube leads to oscil­la­tions, which are felt by the vibra­tion of the mem­brane. The fre­quency of the oscil­la­tion with the lower end in liq­uid helium is notice­ably lower than that when it is in cold gas, allow­ing the liq­uid level to be deter­mined eas­ily (in most cases). The dip­stick should not be left in the cryo­stat when it is not in use because it intro­duces a large amount of heat.