See how polarization can keep a piece of paper stuck to the plotter.

When the auto-grip is turned on, there are alternating stripes of positive and negative charge beneath the plate of the plotter that hold the paper in place.

Seems to be HP 7005B X-Y Recorder.

1. Use tape and a piece of string to hang a weight from the paper over the edge of the plotter (a letter-sized sheet seems able to comfortably hold up at least a 200g weight)
2. Plug in the device and turn the power on to the middle setting
3. Flip the 'Chart' switch from release to hold
4. The paper will stick to the surface even with the mass hanging over the edge

White paper may be hard to differentiate from the plotter surface, so use coloured paper if possible.