When use "top" command to check the memory usage for some process, some times the output will display like "34M+", "15M-". Does that mean "more than 34M"/"less than 15M"? if so, why doesn't use the same sign, like "34M+"/"14M+" , or "35M-"/"15M-"?
No, if it was "more than" or "less than" don't you think they would use the more than or less than signs? If you watched these a bit closer it might become clear as to what is going on. It's indicating when memory is increasing or decreasing on a certain process.