speed calculation

[Joe S]

Ahoy everyone!

I have been trying to get back into SH 3 and 4 and am having some problems. Up to now, I have been calculating speed by doing the time and distance calculation on the Nav map. However, I would like to use the speed calculator on the "attack data tool" in the periscope view. I have viewed a number of video tutorials and have not found one that covers this in detail. Usually wen I try to use the speed calculator I get the message that says " cannot calculate speed need more time between intervals," or something like that. Every once in a while I get a speed estimate, but have not been able to figure out what I am doing right or wrong.
In my version of the game manual, page 63 refers to the "lock button" in periscope view. I have no idea where that lock button is. Cany anyone help me out?

In manual targeting, is a light supposed to go on when we get an accurate solution?

If someone could please post an outline of the proper steps to using the speed calculator, ( for dummies) I would appreciate it!

Thanks!

Joe S