Both the optical and the interpolated resolutions are given in dots per inch or dpi. You need to find out if the 2400 dpi resolution shown on the box is optical or interpolated before comparing prices. Another comparative feature is the number of bits supported by a scanner. The more bits the more image can be handled and processed. The scanners with the highest bits are generally of the best quality, all other things being equal.
Bits relate the number of colors that a scanner can interpret or scan.
The more bits the more colors. The more colors the better the picture. When looking at a black and white scanner the bits relate the the shades of grey supported. The biggest mistake that scanner buyers make when selecting a scanner is to get one with too small optical resolution and too few bits. Most scanner buyers are back in the store within three months buying another scanner with higher capacity in these areas.