Calculating the Sizes of Objects and Distances between Objects in Electron Microscopic Images
The working image printed from the computer or viewed on the monitor has a magnification value embedded in the lower right hand corner of the image to the right of the image number. This magnification is the screen magnification at which the microscope was operating when the image was recorded. It has nothing to do with the printed image or the image as it is seen on a computer screen.
However there is also a magnification bar in the lower left hand corner of the image. This "mag bar" and the specified length it represents in the specimen are generated by the computer when the image is made. Because it is embedded in the image, the mag bar expands and contracts as the image is enlarged or reduced. But the length of the specimen it represents remains constant. By comparison with this mag bar, the size of any object, or the distance between any two objects, can be calculated as follows:
Print a good photo quality image that encompasses the object or distance to be measured (X) as well as the magnification bar in the lower left hand corner of the image.
Measure the distance, or the size of the object in question in millimeters on the print with a ruler or loupe. Set this value equal to "Y".
Next measure the length, also in millimeters, of the magnification bar on the print. Let this length equal "B".
Note the length in the specimen represented by the magnification bar. This is generally expressed in micrometers (µm) or nanometers (nm). Let this value equal "A".
The length or size of interest in the specimen (X) equals A(Y/B) in units specified by the magnification bar.