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.
For example, a check may state, Valid for 90 days from this date or Not valid after 180 days. If you deposit a check that has this notice on it, the check writer's bank will likely refuse to process it because many corporations have rules set up on their bank accounts due to the sheer number of items that flow through.