Knemometry is the technique of choice for short-term growth studies, a
s it is the only anthropometric technique available that allows suffic
iently accurate measurement of the lower leg (in anatomical terms, the
leg) to enable changes in leg length to be detected over as short an
interval as a week or less. The portable knemometer, like the Valk kne
mometer, essentially consists of two main parts: a rigid metal frame h
olding the footplate, measuring ruler and plateau and a moveable chair
that moves on frictionless rollers on a track on the base of the fram
e. Unlike the Valk knemometer there is a standardized seat position fo
r all subjects, making it easier and quicker to use. Assessment of tec
hnical error was done using mean coefficient of variation (CV) of lowe
r leg length measurements done on the portable knemometer. Comparison
of measurements made by two different observers was made by using perc
entage reliability. A small PR implies consistency between the two met
hods or observers being compared. Measurements from 164 visits were us
ed to calculate the machine precision. Mean CV using all four measurem
ents was 0.13% and using only three, having discarded the first, was 0
.11%. Given a mean lower leg length of 246.3 mm for the children studi
ed this translates to a machine precision of 0.32 mm if all four measu
rements are used and 0.27 mm if the last three measurements in the set
are used. The mean difference in lower leg length between observers w
as 0.11 mm. Percentage reliability between the two observers for the p
ortable knemometer was 0.03%. For comparison, PR for standing height a
nd sitting height are 0.37% and 0.86% respectively. PR between the Val
k and the portable knemometer was 0.04%.