1 online resource (vi, 73 pages) ; color illustrations
data file
OCLC
ocn810215629
Title from title screen (viewed Sept. 18, 2012).
"This report was originally written by Irwin Rust in 1968 and published as Education circular 33. It was later superseded by Cooperative information report 5 in 1978, written by Gene Ingalsbe, and has since been revised several times."