5-14 Table 5-1.—Front Panel Controls and Connectors NO. NAME DESCRIPTION 1 LINE switch This is a two-position switch that can be selected for STBY or OPER. When in STBY, the power supply provides power to the oven of the high stability time base to maintain a constant temperature for the crystal. When in OPER, the power supplies normal power to the unit for operation. 2 RESET This button, when pressed, resets the display and internal count to zero. When pressed continuously, this button lights all segments of the LED display and all annunciator LEDs for a LED test. FUNCTION This is a 10-position selector used to select the mode of operation. FREQ A This position, when selected, allows the counter to measure frequency at channel A. FREQ C This position, when selected, allows the counter to measure the frequency at channel C. PER A This position, when selected, allows the counter to measure the period at channel A. PER AVG A This position, when selected, allows the counter to make a period average measurement of the signal at channel A. The number of periods over which the average is made is determined by the RESOLUTION switch selection. T. I. AVG A!B This position, when selected, allows the counter to make a time interval measurement of a signal applied to channel A. The number of time intervals over which the average will be made is determined by the RESOLUTION switch selection made. T. I. A!B This position, when selected, allows the counter to make a time interval measurement. The start signal would be applied to channel A and the stop signal applied to channel B. 3 CHECK This position, when selected, applies a 10-MHz signal to the decade counting assemblies, verifying operation of the SAMPLE RATE control, RESOLUTION switch, and RESET. RATIO C/A This position, when selected, allows the counter to measure the ratio of the frequency at channel C to the frequency at channel A. RATIO B/A This position, when selected, allows the counter to measure the ratio of the frequency at channel B to the frequency at channel A. 3 Continued Top This position is blank and has no function. This is an eight-position switch that is used to select the resolution in frequency measurements and N for totalizing and averaging measurements. This also determines how long the main gate is open for frequency measurements. 4 FREQ RESOLUTION, N N 1 10 10² 10³ 10⁴    10⁵      10⁶      10⁷ GATE TIME (seconds)   1×10^-6   10×10^-6    100×10^-6   1×10^-3         .01         .1     1      10      RESOLUTION (Hz) 1 M 100 k 10 k 1 k 100 10 1 .1 5 SAMPLE RATE control This is used to vary the time between measurements continuously from approximately 2 milliseconds to an indefinite hold of the display. 6 500 MHz, 50 " This is the channel C input connector. 7, 14 OUTPUT MARKER These are the channel A and B Schmidt trigger outputs used to indicate when a channel is triggered by 0 to 300 mV levels with less than 20 nanoseconds delay.