1-2. The Model 7250A is a Universal Counter-Timer capable of measurements in seven modes of operation: frequency (Channel A, 5 Hz to 80 MHz), period and period averaging (Channel A, 5 Hz to 1 MHz), time interval (Channel A to Channel B, 5 Hz to 2 MHz), counts per minute (Channel A, 5 Hz to 80 MHz), ratio of Channel A (5 Hz to 80 MHz) divided by Channel B(5 Hz to 1 MHz), and totalize Channel A (5 Hz to 80 MHz). In addition, Self Check mode is-provided to demonstrate operability of most 7250A circuits. 1-3. This manual documents the 7250A Universal Counter-Timer under two categories. The standard instrument without options and accessories is covered in Sections 1 through 5, 7 and 8. All optional or accessory items are documented in Section 6; refer to Table 1-1 and 1-2 for a listing of available options and accessories. Schematic diagrams for the standard instrument and the options are centralized in Section 8. 1-4. DESCRIPTION 1-5. The Model 7250A is a seven-digit universal counter-timer capable of measurements in frequency, period, period average, time interval, totalize, ratio, and self check mode. In addition, counts per minute mode offers a direct readout of RPM when the instrument is attached to an appropriate transducer. The 7250A features six manually selected resolution settings, autoranging, leading zero suppression, full annunciation, autoreset, and a free-air crystal time base. 1-6. Each of the two 1 Mfl input channels is controlled by a ± slope control and a three position trigger level offset switch. Separate attenuation controls (continuously variable from X1 to X100) are provided for each input. A 100 kHz low pass filter can be applied to both channels. Channel A can be measured in common with, or separately from, Channel B. Input frequencies on Channel A can range from 5 Hz to 80 MHz. Channel B, when used in ratio and time interval measurements, has a maximum input of 2 MHz. 1-7. A number of options and accessories are available with the instrument. Improved time base stability can be realized with the optional TCXO, or with one of the oven time bases.