Number of exposures remaining in the memory card
The control panel and viewfinder show the number of photographs that can be taken at current settings (values over 1000 are rounded down to the nearest hundred; e.g., values between 2100 and 2199 are shown as 2.1k).
Number of exposures remaining in the buffer memory
When the camera shutter-release button is pressed halfway, the display changes to show the remaining number of images that the buffer memory can hold at current settings before it’s full. When the buffer is full, shooting will temporarily stop until the images have been processed, then as buffer space becomes available shooting can continue. Buffer capacity varies depending on the camera and the image quality and size set.
"r12" indicates that the camera buffer has available space for 12 more photographs at the current image quality settings, "r20" would indicate space for twenty photographs and so on. As the amount of compression varies between photographs, the number remaining in the buffer is an estimation. The estimation is based on the minimum number of photographs remaining so the actual number possible can be higher.
When the users finger is released from the shutter-release button, the display reverts back to the number of photographs that can be saved to the memory card at current settings.