whats your favorite way to calculate speed?

[Dustyboats]

Providing you are dived, your passive sonar gives you a bearing. Use the "marker" to place an "X" at the extreme end of that bearing and note "time".. As the bearing rate alters, place another and so on until you have about 6 or 7 "X's". They may seem to be scattered but you can take a mean line through them, using the "ruler". This should give you a fairly accurate course of the target until you close to your "prior to aiming point". Having those "X's" timed you can now work out speed by taking the "compass" tool and get "distance travelled by target" measuring from your first "X" marker to your last......in so much time, (which you have noted), target has travelled so many nm or meters(or parts of)...you have your speed to within + or - 1Knt.