Even further, continuously switching these values between each raster line, instead of once per frame, will divide by 2 the difference between the 2 positions and so will give an offset of a quarter of a CRTC character.
And smartly combining R2 and R3 horizontal screen wobbling effects at every raster line will give 1-pixel mode1 horizontal hardware scroll. See the CRTC Compendium for more details.
As these effects rely on invalid video signals, they are badly supported on modern displays.