When using a vertical angle from some high object, such as the truck to the waterline it is necessary to observe the waterline at a point immediately below the high object.
Xa usebenzise i-engile eme nkqo kwinto ephezulu, njengetraki kumgca wamanzi kuyimfuneko ukuqwalasela umgca wamanzi kwindawo ngokukhawuleza ngasezantsi kwento ephezulu.