Frequency is measured in hertz (Hz). A person who has hearing within the normal range can hear sounds that have frequencies between 20 and 20,000 Hz. The most important sounds we hear every day are in the 250 to 6,000 Hz range.
An issue date was added, and cheques may not be valid a certain amount of time after issue. In the US and Canada a cheque is typically valid for six months after the date of issue, after which it is a stale-dated cheque, but this depends on where the cheque is drawn; in Australia this is typically fifteen months.
RE: ff: Most checks are stale dated after 6 months, unless specified by the check. IE: Not valid after 90 days or something similar. However, say for instance you wrote a check in December of last year and the person you wrote it to just cashed it yesterday. When you get your monthly statement for July, you can dispute anything on your account for up to 60 days past the date you received your statement.