GE Vscan Air Manual page 399

Measurement accuracy (continued)
Table 8-2: Measurement accuracy - Linear array (shallow scanning) transducer
Measurement
Axial
Lateral
Circumference (ellipse)
Speed of Sound in Tissue
–
Vscan Air User Manual
Direction GP092020-1EN Rev 18
Unit
Distance
cm or mm
cm or mm
cm or mm
The ellipse circumference is calculated via the below formula
from §16 in Ramanujan, Srinivasa (1914), "Modular Equations
and Approximations to
372. ISBN 9780821820766.
The average value 1540 meters / second is used for all
calculations. Depending on the tissue structures, this
generalization may give errors from 2% (typical) to 5% (much
fatty tissue layers present).
Measurement accuracy
Useful range
1mm-60mm ±0.5mm or ±3% whichever is
greater
2mm-40mm ±1mm or ±5% whichever is
greater
5mm-150mm ±5% or ±1mm whichever is
greater
". Quart. J. Pure App. Math. 45: 350–
Accuracy
8-17