Epson PERFECTION 1240U Reference Manual page 78

Units menu:
Select a unit of measurement. You can select either inches, pixels,
or cm.
Storage size indicator:
The storage size of an image is indicated in KB or MB. As you
change the image area in the Preview window, this value also
changes.
Lock button:
The current size of width-to-height of the target image can be
locked, allowing the ratio of width-to-height of the Source image
to change according to the scale value, or the scale value to change
according to the ratio of width-to-height of the Source image. This
is especially useful in cases where the size of an image does not
fit the size of the paper on which you want to print the image, but
you want to keep the image's original proportions. Enter the size
of the paper in the Width and Height fields of the Target box and
then click the Lock button. The scale value is automatically
changed, maintaining the current ratio of width-to-height to fit
the paper.
Resolution:
The resolution for the current scanning operation can be changed
by selecting a resolution or typing in the value. This setting
overrides the resolution setting you make in the Destination
dialog box.
3-18
Understanding EPSON TWAIN Features