How to setup an scale in imageJ?

Hi,
I am able to setup an scale but seems the measurement in not accurate. What is the best way to calibrate the measuring scale in imageJ.
Your assistance will be appreciated.

Hi,

what exactly do you want to do? Setting the scale/pixel size of an uncalibrated image by means of some object in the image (with a known size)? Or is it an image of a microscope, with some chance to retrieve the pixel size form image metadata or hardware?

Hi,
Thank you for your reply. I have already the microscopic image (10x). I did not measure with any scale before. Now is that possible to calibrate and set a scale.

Apart from the magnification of the objective, you need to know the total magnification of the microscope (i.e., including auxiliary magnifications and camera adapters, which often introduce an additional magnification of 0.5-1.0x) and the pixel size of the camera. Then, the size of a pixel of the image is the total magnification divided by the pixel size of the camera, and this value can be set in ImageJ (with the menu command Image → Properties). Did you save the image(s) in the format suggested by the microscope manufacturer (e.g., Zeiss .czi, Leica .lif…)? These images usually carry all the required information in their metadata. The Bio-Formats plugin reads it and sets the pixel size automatically.