Furuno CI-68 - Manual (Page 68)

PRINCIPLE OF OPERATION
AP-12
Tide differential calculations in water tracking mode
Tide speeds of layer A (C1) and layer B (C2) relative to near-surface layer (Vw) are
calculated as follows:
Tide differential based on layer A (speed of layer B as viewed from layer A)
D1 = Vw - Vwa (Speed of layer A based on near-surface layer)
D2 = Vw - Vwb (Speed of layer B based on near-surface layer)
The tide differential (Dd) between layers A and layer B is;
Dd = D2 - D1
= (Vw - Vwb) - (Vw - Vwa)
= Vwa - Vwb
= 8 - 5
= 3 (kt)
OR
Tide differential based on layer B (speed of layer A as viewed from layer B)
Dd = D1 - D2
= (Vw - Vwa) - (Vw - Vwb)
= Vwa - Vwb
= 5 - 8
= -3 (kt)
If you compare the results of calculations on this page with the ones on preceding pages,
you will find the tide differential of two layers is identical irrespective of tracking mode.