A method comprising: synchronizing a three-dimensional measurement device configured to measure coordinates of points on physical parts in a three-dimensional space and having a 3DM internal 3D coordinate system O 3DM, X 3DM, Y 3DM, and Z 3DM, with a hand-held intelligent guidance device that is physically separate from the 3DM, the IGD having a processing unit, a display device, a gravity direction measurement device, an electronic compass, a three-axis accelerometer and an IGD internal 3D coordinate system O IGD, X IGD, Y IGD, Z IGD, the synchronizing comprising: determining coordinates RPX IGD, RPY IGD, RPZ IGD of a reference point RP in the IGD internal 3D coordinate system O IGD, X IGD, Y IGD, Z IGD; defining a coordinate system O Earth, X IGD-Earth, Y IGD-Earth, Z IGD-Earth using a direction opposite to gravity as Z IGD-Earth and a direction corresponding to a magnetic north pole as Y IGD-Earth, from a perspective of the IGD; computing and applying a rigid transformation T IGD-To-IGDEarth to transform axes X IGD, Y IGD, Z IGD of the IGD internal 3D coordinate system to X IGD-Earth, Y IGD-Earth, Z IGD-Earth and the reference point RP having the coordinates RPX IGD, RPY IGD, RPZ IGD to O Earth; determining coordinates RPX 3DM, RPY 3DM, RPZ 3DM of the reference point RP in the 3DM internal 3D coordinate system O 3DM, X 3DM, Y 3DM, and Z 3DM; defining a coordinate system O Earth, X 3DM-Earth, Y 3DM-Earth, Z 3DM-Earth using a direction opposite to gravity as Z 3DM-Earth and the direction corresponding to the magnetic north pole as Y 3DM-Earth, from a perspective of the 3DM; and computing and applying a rigid transformation T 3DM-To-3DMEarth to transform axes X 3DM, Y 3DM, and Z 3DM of the 3DM internal 3D coordinate system to axes X 3DM-Earth, Y 3DM-Earth, Z 3DM-Earth and the reference point RP having the coordinates RPX 3DM, RPY 3DM, RPZ 3DM to O Earth; and displaying, using the display device of the IGD, 3D graphics in a 3D coordinate system synchronized with a 3D coordinate system of the 3DM. synchronizing a three-dimensional measurement device configured to measure coordinates of points on physical parts in a three-dimensional space and having a 3DM internal 3D coordinate system O 3DM, X 3DM, Y 3DM, and Z 3DM, with a hand-held intelligent guidance device that is physically separate from the 3DM, the IGD having a processing unit, a display device, a gravity direction measurement device, an electronic compass, a three-axis accelerometer and an IGD internal 3D coordinate system O IGD, X IGD, Y IGD, Z IGD, the synchronizing comprising: determining coordinates RPX IGD, RPY IGD, RPZ IGD of a reference point RP in the IGD internal 3D coordinate system O IGD, X IGD, Y IGD, Z IGD; defining a coordinate system O Earth, X IGD-Earth, Y IGD-Earth, Z IGD-Earth using a direction opposite to gravity as Z IGD-Earth and a direction corresponding to a magnetic north pole as Y IGD-Earth, from a perspective of the IGD; computing and applying a rigid transformation T IGD-To-IGDEarth to transform axes X IGD, Y IGD, Z IGD of the IGD internal 3D coordinate system to X IGD-Earth, Y IGD-Earth, Z IGD-Earth and the reference point RP having the coordinates RPX IGD, RPY IGD, RPZ IGD to O Earth; determining coordinates RPX 3DM, RPY 3DM, RPZ 3DM of the reference point RP in the 3DM internal 3D coordinate system O 3DM, X 3DM, Y 3DM, and Z 3DM; defining a coordinate system O Earth, X 3DM-Earth, Y 3DM-Earth, Z 3DM-Earth using a direction opposite to gravity as Z 3DM-Earth and the direction corresponding to the magnetic north pole as Y 3DM-Earth, from a perspective of the 3DM; and computing and applying a rigid transformation T 3DM-To-3DMEarth to transform axes X 3DM, Y 3DM, and Z 3DM of the 3DM internal 3D coordinate system to axes X 3DM-Earth, Y 3DM-Earth, Z 3DM-Earth and the reference point RP having the coordinates RPX 3DM, RPY 3DM, RPZ 3DM to O Earth; and determining coordinates RPX IGD, RPY IGD, RPZ IGD of a reference point RP in the IGD internal 3D coordinate system O IGD, X IGD, Y IGD, Z IGD; defining a coordinate system O Earth, X IGD-Earth, Y IGD-Earth, Z IGD-Earth using a direction opposite to gravity as Z IGD-Earth and a direction corresponding to a magnetic north pole as Y IGD-Earth, from a perspective of the IGD; computing and applying a rigid transformation T IGD-To-IGDEarth to transform axes X IGD, Y IGD, Z IGD of the IGD internal 3D coordinate system to X IGD-Earth, Y IGD-Earth, Z IGD-Earth and the reference point RP having the coordinates RPX IGD, RPY IGD, RPZ IGD to O Earth; determining coordinates RPX 3DM, RPY 3DM, RPZ 3DM of the reference point RP in the 3DM internal 3D coordinate system O 3DM, X 3DM, Y 3DM, and Z 3DM; defining a coordinate system O Earth, X 3DM-Earth, Y 3DM-Earth, Z 3DM-Earth using a direction opposite to gravity as Z 3DM-Earth and the direction corresponding to the magnetic north pole as Y 3DM-Earth, from a perspective of the 3DM; and computing and applying a rigid transformation T 3DM-To-3DMEarth to transform axes X 3DM, Y 3DM, and Z 3DM of the 3DM internal 3D coordinate system to axes X 3DM-Earth, Y 3DM-Earth, Z 3DM-Earth and the reference point RP having the coordinates RPX 3DM, RPY 3DM, RPZ 3DM to O Earth; and displaying, using the display device of the IGD, 3D graphics in a 3D coordinate system synchronized with a 3D coordinate system of the 3DM.