If this is for calibrating a home made CRO for the first time, you need a good reference for your voltage and time. For voltage a DVM should do, for time, the 50 HZ from the mains will do for the lower time base speeds. Then you need some sort of oscillator which is calibrated, or a very good way would be to use a high frequency crystal oscillator which is followed by some decade dividers.
So you get a transformer to give you some low voltage output, say 12v, put a pot across the secondary winding and monitor the tapped of voltage with your DVM and compare its reading with your Y deflection. Remember that the DVM will read the RMS voltage while the peaks of the sine wave as viewed will be 1.414 times as greater. i.e. set the voltage to read .707 on your DVM, this gives you a 2V peak to peak deflection on the CRO. If you need a much smaller signal, follow this with a 10: 1 or 100 :1 voltage divider using 1% 100K, 10k and 1K resistors.
Frank