Just found from another discussion :
“The Yestech (pattern match) is very easy to program and use but it took sooooo much up-keep to keep the false calls to a manageable amount. The CyberOptics (also Omron) is more of an algorithm based type of machine and it takes a long time to program from scratch when comparing to the YesTech, but I've found that up-keep is waaaaay less with this type of machine and false calls are very minimal and much easier to keep down. So higher level of false calls means higher level of operator escapes ?defective board at customer site.”
(http://www.smtnet.com/Forums/Index.cfm?CFApp=1&Message_ID=66199)