It is necessary to power cycle the connected camera (turn off and on) in order to see the updated shutter count value. This is due to a technical optimization that minimizes battery power drain when a camera is connected to eosmsg.

Using numeric suffix of filenames written by the camera on a flash card is not equivalent to camera's shutter count (the suffix resets to 0 after 9999). Here are examples when the filename does not indicate the true number of pictures taken with the camera.

• A new flash card is inserted containing a picture file with higher numerical suffix. The numbering then continues with this higher suffix. For example, if the last file written by the camera was IMG_3750.JPG, this indicates that the shutter count is 3750. If a new flash card is inserted with a file IMG_4100.JPG, then the next picture taken with the camera will be written under IMG_4101.JPG. The shutter count in this case will be only 3751.
• If a blank flash card is inserted afterwards, some cameras like the Canon 60D will continue previous filename numbering; for example, will write file IMG_4102.JPG when shutter count is 3752. The file name is edited to lower the numerical suffix. Some cameras, such as the Canon 5D Mark II, will use the card filename to construct the name for the next picture. This results in a much lower perceived shutter count than the true shutter count. For example, let's say the filename is edited from IMG_9000.JPG to IMG_2000.JPG. The next picture file written by a camera like Canon 5D Mark II will be IMG_2001.JPG. The perceived shutter count is 2001, whereas the real shutter count is 9001.
• Pictures are taken when the camera is connected directly to a computer (without a flash card inside).

Due to the real-time viewing and video shooting the shutter is in a normally open state, the mirrorup count alwasys wil be greater than shuttercount. so the number of mirror count can more accurately reflect the situation of the camera.