A small brochure that goes into the shipment box.
Edits:

Frequency Counter : 10Hz to 16MHz . Amplitude minimum +/-50mV
Digital Inputs : 5V tolerant . Do not exceed

CH3 : +/-3.3 Volts . 1MOhm input impedance. It passes through a non inverting, unity buffer, and its gain can be controlled by connecting Rg to GND via a resistor.

MIC : +/-15mV signal. 200x gain stage inside.