Hi,
I got  a BK Predision oscilloscope no.1478.
I don't use a grd wire I just use the positive and it gets ac signal
and a SQUARE wave from my signal gen.
But I cann't get the volt from a dc battery.I just can't find a display
on it. I don't know how to set it. I set the volt to 10 volts and trying to
display it on the oscilloscope and nothing.Hi

If you want to measure a DC voltage on an  oscilloscope you NEED to use the ground wire and the center of the probe. If you don't use the ground wire how are you going to get the return path for the voltage.
Also the input COUPLING needs to be set to DC By default it is set to ACThis is a hardware question.
Here is a Google SEARCH:

how to use oscilloscope to measure dc voltage

You will find videos and other links.
In order for ANY measuring device to measure DC voltage, it needs to have a reference to ground so the ground connection is absolutely needed.Thanks all, I got it figured out. My a channel won't put a display line on computer.
The b channel will and I can measure volts dc while I'm on both channels.
But they both seem to work on ac cycles and square wave ok.
It took me a day to get aquainted. You were a great help.