To set the clock time. The clock has counter circuits not only for hours and minutes, but also for seconds (and sub-seconds) though display digits are not given for seconds. The time kept by the clock counter circuits can be set with three pushbutton switches FastAdv, SlowAdv and ClearSec. The FastAdv and SlowAdv switches are both related to the hours/minutes counter and not to the seconds counter.

• Pushing FastAdv advances the hours/minutes counter at about 100Hz rate (i.e., advances at the speed of about 100 counter-minutes par 1 real second).
• Pushing SlowAdv continuously advances the hours/minutes counter at about 5Hz rate (i.e., advances at the speed of about 5 counter-minutes par 1 real second). Here, 'continuously' means more than about 0.7 second.
• Pushing SlowAdv instantaneously advances the hours/minutes counter by 1 (i.e., advances by 1 counter-minute par single stroke of the switch). Here, 'instantaneously' means less than about 0.7 second.

• Pushing ClearSec makes the seconds counter cleared to zero, and keeps the seconds counter at zero while the ClearSec switch is pushed. To show clearly the acceptance of ClearSec request, the colon is designed to disappear during ClearSec switch is pushed. Carry to the minutes and hours digits is not generated with this clear operation.

Battery back-up. The clock is usually operated with AC line power, and has a 9V battery of 6F22, 6LF22 or 6LR61 for back-up purpose. If power failure occurs at AC line, the clock does not display the time, but continues counting the time with the aid of battery power. If you do not need the battery back-up function, the battery need not be installed.
Attention: Do not touch pushbutton switches FastAdv, SlowAdv and ClearSec under the condition that the power is not supplied from AC line. The reasons are as follows. The clock time setting functions (functions related to these switches) are not inhibited even in battery operation at power failure, though the clock setting functions are not expected to be correctly used without help of display in operation. In addition, current drawn from the battery under power failure condition is increased by a few mA when these functions are in use, and increased current drawing may result in a significant battery voltage drop (if battery is already much used) which causes initialization of the clock status (see below) and loses the time kept by the clock.

Battery maintenance. Since the clock does not have a circuitry to monitor the battery condition and battery maintenace depends fully on the user, somewhat detailed explanation will be in order. The battery back-up is expected to function if the battery voltage is greater than 6V (with drawing 1-2mA current) for the set constructed with typical characteristic components. The clock set draws only negligible current (in comparison with battery's self-discharge) from the battery while AC power is supplied. When power failure occurs at AC line, the clock consumes about 1mA current (in case the components used are of typical characteristic devices) from the battery. Taking these into account, one can expect battery life to extend for 1 to 2 weeks of total amount of AC power failure period with the 9V alkaline battery (6LF22/6LR61). So, replacing the battery will not be required for a few years unless power failures have occured frequently or power failure that has continued long time is experienced. However, the user who needs reliable battery back-up is advised to check the battery condition occationally with using appropriate tool. The battery unit whose EMF is measured as low as 7.0-7.5V or less should be replaced with a fresh battery. No problem is caused by the presented design even if the battery is replaced while the clock is in operation. Reverse polarity connection of battery does not damage either the clock set or installed battey (under such a condition, simply the battery back-up does not function).

Initial state. If the power is not supplied from the AC power line and the battery energy is also exhaust, the clock cannot keep counting the time. If such a condition is detected by the clock itself, the hours/minutes/seconds counter is initialized to 0:00:00 (display shows '0 00' without colon) when the power recovers. This initial state continues until the FastAdv or SlowAdv switch is pushed. The hour 0 appears only after this initialization; the carry from minutes generated in the normal clock operation updates the hours counter state among 1, 2, ... , 12 in the usual rule of 12-hour format representation.