An MRI address rule has both an offset and a slope; three rows show which part moved. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Base one tesla gives four, eight, twelve hertz
With base field 1 tesla and gradient 1 tesla per metre, positions 0, 1, 2 metres give frequencies 4, 8, 12 hertz.
f=4(Bbase+Gx)=4,8,12
Raising only the base field shifts every frequency
Keeping gradient 1 and raising base field to 2 tesla changes the frequency row to 8, 12, 16 hertz.
f=4(Bbase+Gx)=8,12,16
Raising only the gradient spreads the addresses
Returning base field to 1 and using gradient 2 makes the frequency row 4, 12, 20 hertz.