2 Terms
2.0.1 Distance Deviation
It represents the allowable erection deviation of the relative size between boiler steel structures/equipment components design center lines（such as between the pillars，between cross beams or between waterwalls and steel structure and so on）.
2.0.2 Diagonal Deviation
It represents the length difference of two diagonal lines between the crossing points of the longitudinal and transverse center lines for square or rectangle shape design of boiler steel structures/equipment components（such as the foundation，pillars，furnace and so on）.
2.0.3 Elevation Deviation
It represents the difference between the erection height of boiler steel structures/equipment component and its design elevation，generally on the basis of the elevation of the steel frame 1m.The qualified measurement tools or instruments after metrological verification shall be used uniformly for each section of boiler proper（steel frame，metal structure，heating surface，6 ducts，boiler setting insulation and so on）.
2.0.4 Depth of Parallelism
It represents the parallel degree between two parallel lines or planes，whose deviation shall be the difference between the both-end minimum vertical distances.
2.0.5 Verticality
It represents the difference between the angle of the vertical axial line and the plane or two planes and the right angle，whose deviation is represented by the included angle between the axial line or plane and the ideal vertical line，or by the ratio of the reference vertical axial line unit length to the minimum distance of the measured line or plane，for exampleΔ/m.
2.0.6 Relative Misalignment
It represents that there is a deviation between the installation positions of two objects（such as components，pipe fittings and so on）and the design center line position and the deviation directions are opposite，the relative misalignment is the sum of absolute values of two deviations.or although the deviation directions are the same，the deviation values are different，the relative misalignment is the difference of absolute values of two deviations.
2.0.7 Concentricity
It represents that two circular objects erected at the same center axis（such as the end cover and tank body of ball mill，the center line of both-end hollow shafts and the tank center line，the neck joint of air duct rotating section in rotary air heater，the moving blade adjusting device of the fan and so on）are required to be concentric，and the concentric degree is the distance between two circle centers.
2.0.8 Roundness
It represents the deviation between the circumference（part or local）of the large circular object（such as the stator or rotor of rotary air heater，rotary air hood，fan cover and so on）and the corresponding ideal circumference.
2.0.9 Flatness
It represents the maximum difference between the local salients and the local depressions in the same plane of the erection component.
2.0.10 Planeness
It represents the degree of one plane deviating from the corresponding ideal plane.For equipment plane（such as waterwalls and so on），this deviation is the measuring distance between two concave-convex parallel planes.For boiler setting or the insulation plane，it is represented byΔ/m.
2.0.11 Radial Run-out
With vertically pointing the dial indicator to the axle center of the measured section and moving the rotor，the difference between the maximum and minimum values of each point reading in the measured plane（8 or 16 equal diversion points in general）is defined as radial run-out.
2.0.12 Axial Run-out
It is also called as"the spoon shaped deflection of end surface"on the given diameter circumference of the measured end face.Putting the dial indicators at two positions with the relative included angle of 180°and moving the rotor，the axial run-out value（or called as the spoon shaped deflection value）is a half of the difference between the maximum difference and the minimum difference of the simultaneous readings in two dial indicators.
2.0.13 Horizontal Deviation
It represents the deviation difference of the longitudinal and transverse horizontal centerline of boiler steam drum，header and other equipment.（before erection，check the position of dotting punches marked with horizontal lines by the manufacture）.It shall be checked whether the four-side dotting punches are erected in the same level.The altitude difference between two points respectively in longitudinal/transverse horizontal centerlines is defined as（longitudinal/transverse）horizontal deviation.
2.0.14 Ellipticity
It represents the ration of the difference between the maximum and minimum diameters in some transverse section of the cylindrical shaft or hole（ring）to nominal diameter in percentage.The circle center of the ellipticity is unfixed，and the maximum and minimum diameter may be in any direction.
2.0.15 Levelness
It represents the level difference degree of the objects erected in the same level，which is the absolute difference between the measured values of different points generally by using the level bar，the level instrument or U-shaped tube and so on.