1. A method for substituting at least one high quality position measurement of an object taken before an interrupting event with a set of upgraded low quality position measurements of said object provided by the same source of measurements after said interrupting event; said method comprising the steps of: (A) obtaining at least one high quality position measurement of said object provided by a source of measurements before said interrupting event; said source of measurements before said interrupting event is selected from the group consisting of: {a carrier differential Satellite Positioning System SATPS; a code differential SATPS; an autonomous SATPS; an Inertial Navigation System (INS); and a Pseudolite-Based Positioning System}; (B) saving said at least one high quality position measurement of said object by using a memory block; (C) if said at least one position measurement of said object provided by said source of measurements after said interrupting event is of substantially high quality; or if each said position measurement of said object provided by said source of measurements after said interrupting event is of low quality, and if there is a restoration event, and if at least one said position measurement of said object provided by said source of measurements after said restoration event is of substantially high quality; then using said at least one position measurement of substantially high quality of said object for navigation purposes of said object obtained in said step (A); and (D) if each said position measurement of said object provided by said source of measurements after said interrupting event is of low quality, and if there is not at least one restoration event; or, if each said position measurement of said object provided by said source of measurements after said interrupting event is of low quality, and if there is a restoration event, and if each said position measurement of said object provided by said source of measurements after said restoration event is of low quality; then upgrading said at least one position measurement of said object by using an upgrade algorithm; said upgrade algorithm comprising at least the following steps: (D 1 ) if a set of Correction Terms is substantially unavailable, computing said set of Correction Terms; wherein said set of Correction Terms comprises a set of error estimates of said at least one low quality position measurement; (D 2 ) if said set of Correction Terms is substantially available, computing at least one system quality metric; wherein each said system quality metric indicates whether or not said set of Correction Terms is substantially adequate for upgrading purposes; (D 3 ) if each said system quality metric indicates that said set of Correction Terms is substantially adequate for upgrading purposes; setting a flag indicating said set of Correction Terms is substantially adequate for upgrading purposes, using said set of Correction Terms to upgrade said at least one low quality position measurement of said object to obtain said at least one upgraded position measurement of said object and outputting said at least one upgraded position measurement of said object; (D 4 ) if at least one said system quality metric indicates that said set of Correction Terms is substantially inadequate for upgrading purposes, setting a flag indicating said set of Correction Terms is substantially inadequate for upgrading purposes, and checking whether said set of Correction Terms can be updated to become substantially adequate for upgrading purposes; (D 5 ) if said set of Correction Terms is updatable to become substantially adequate for upgrading purposes; updating said set of Correction Terms, using said set of updated Correction Terms to upgrade said at least one low quality position measurement of said object to obtain said at least one upgraded position measurement of said object, and outputting said at least one upgraded position measurement of said object; and (D 6 ) repeating said steps ((D 1 )-(D 5 )) for each next epoch of position measurement of said object; wherein each said low quality position measurement of said object includes an epoch timing coordinate indicative of when said low quality position measurement of said object was taken; and wherein said at least one position measurement of said object is of low quality if said low quality position measurement of said object includes an unacceptable error in said position measurement of said object, or is not substantially recent.