Speed log data

Speed log data is formatted in the following sentences:

$VHW,x.x,T,x.x,M,x.x,N,x.x,K*hh

VHW sentence fields
Item definition units
x.x degrees true ?
T T=true n/a
x.x degrees Magnetic ?
M M = Magnetic n/a
x.x Speed of vessel relative to water Knots/hour
N N = Nots n/a
x.x Speed of vessel relative to water Km/hour
K K = Kilometers n/a
Checksum n/a n/a

$VBW,x.x,x.x,A,x.x,x.x,A*hh

VBW sentence fields
Item Definition Units
x.x Longitudinal water speed, "-" means astern ?
x.x Transverse water speed, "-" means port ?
A A = Data Valid n/a
x.x Longitudinal ground speed, "-" means astern ?
x.x Transverse ground speed, "-" means port ?
A A = Data Valid n/a
Checksum n/a n/a