In order to reduce confusion about a displayed absolute altitude and to enhance reliability and correctness, the present invention provides a display method of an altitude display apparatus for displaying an absolute altitude wherein an initial atmospheric pressure is detected, and an absolute altitude is calculated and displayed based on a pressure difference between the initial atmospheric pressure and a current atmospheric pressure if the detected initial atmospheric pressure is larger than a predetermined atmospheric pressure.

An accumulating altimeter includes a programmable accumulator which selectively accumulates altitude changes from a reference altitude in accordance with accumulation thresholds. Altitude changes in the direction of interest, e.g. altitude gains, are accumulated once a non-opposing accumulation threshold has been reached. Opposing altitude changes which are less than an opposing accumulation threshold are used to offset non-opposing changes. Opposing altitude changes which are equal to or greater than the opposing accumulation threshold are used to re-establish the reference altitude, whereafter accumulation of non-opposing altitude changes resume after the non-opposing accumulation threshold has been reached.

A compact altitude and rate of descent instrument is combined with a visual indication device and attached directly as a self-contained unit to protective eye wear or headgear for the determination of critical altitudes while engaged in freefall skydiving without the need for head or hand movements. Such an instrument reduces potentially fatal lack of altitude awareness due to extraneous factors and allows for more complete concentration on maintaining eye contact with others when performing maneuvers in close proximity such as during freefall formation flying (relative work).