  Several items on the diagnostics and interpretation of coronal loop
observations are under debate. In this work, we analyze a well-defined loop
system detected in a time-resolved observation in several spectral bands. The
dataset includes simultaneous images in the TRACE 171 A, 195 A and 284 A bands,
and Yohkoh/SXT, and two rasters taken with SoHO/CDS in twelve relevant lines.
The loop is initially best visible in the TRACE 195 A filter band, and later in
the 171 A filter band, with correspondence with the CDS raster images at log T
\~ 6.0-6.1. We have taken as pixel-by-pixel background the latest TRACE, Yohkoh
and CDS images where the loop has faded out. We examine the loop morphology
evolution, the light curves, the TRACE filter ratio distribution and evolution,
the images and emission measure from the CDS spectral lines. Our analysis
detects that, after background subtraction, the emission along the loop and its
evolution are non-uniform, especially in the 171 A filter band, and that the
TRACE 195/171 filter ratio has a moderately non-uniform distribution along the
loop and evolves in time. Both the light curves and the filter ratio evolution
indicate a globally cooling loop. Relatively hot plasma may be present at the
beginning while, during the first CDS raster, the data indicate a rather
moderate thermal structuring of the loop. Our data analysis supports a coherent
scenario across the different bands and instruments, points out difficulties in
diagnostic methods and puts quantitative basis for detailed forward modeling.
