Why two GPS on ship show slight different positions ?

Two GPS on ship show slight different positions due to following reason mentioned below –

it’s not because their antennas are separated by some distance.

– Each GPS receiver has its own clock which are less stable which means each receiver has its own clock error and when it solves the equations to determine the precise position of the receiver

                            i.e. d= s x Δt

where ‘s’ is speed of light (3 X 10 meters per second) and ‘Δt’ is the time difference(Δt) between data transmitted from different satellites and its reception at the receiver. ‘Δt‘ varies for each GPS resulting in the different values of ‘d ‘& hence slight difference in the position.