Even if you are able to get both instruments to read the same, be very wary about the information they suggest, it does not necessarily mean that it will place you in the right location according to your paper charts of the area. There is an excellent guide contained within chapters 1 and 2 of "The Mariners Handbook Np 100" which is produced by the United Kingdom Hydrographic Office where, as far as I am aware, the latest version of that book is Edition 9. You can download a free copy of edition 8 at the following address
http://www.libramar.net/news/np_the_mariners_handbook/2012-03-13-547 Essentially what it means is that despite charts being referred to as WGS84, only the latitude and longitude scales on those charts are guaranteed to be correctly placed, whereas the charted details within the chart may not be more correctly placed than was determined at the time that the area was originally surveyed. That could have been back in the middle of the 19th century at a time when there were no electronic navigation systems and no radio time signals to enable a ships chronometer to be checked for accuracy (essential for determining Longitude).
A simple check you can carry out is to look at your chart plotter before you leave your berth and see whether it shows your position correctly in relation to where you are in the marina. Be aware that in some parts of the world there are areas where the difference between GPS positions and features shown on local charts can differ by as much as seven miles !!! If that seven miles contains shallows or rocks that you can run aground on, the apparent umpteen decimal point accuracy of GPS will not keep you safe.
The photo below shows the last paragraph of chapter 2 section 4 of the 9th edition of The Mariners Handbook published by the UKHO.
