Technical riddle: “One site writes 15,000, and the other 15,001!”

In the workshop, photographers sometimes show me two screenshots of different web services: *“Look, on one site I was given 15,000, but on yours it’s 15,001. Why did this difference arise?”*.

Let me, as a parser developer, break down all 3 reasons for the discrepancy in numbers.

3 Reasons for the difference in results in reports

1. Enabling zero frame (Zero-indexing vs 1-indexing)

In some old Nikon DSLRs, the first test shutter operation on the factory bench is designated as `0`, in others as `1`. The difference of one is the mathematical difference in the calculation of arrays by programmers of different sites.

2. Confusion between MechanicalShutterCount and TotalShutterCount (Mirrorless Z cameras)

If you run a frame from Nikon Z6 through a simple universal site, it will display the value of the `TotalShutterCount` tag (for example, 120,000 frames, including quiet ones). Our specialized service reads exactly `MechanicalShutterCount` (for example, 15,000 frames of mechanical curtains).

The difference of 105,000 frames is not an error, but a different physical meaning of the fields being read!

3. Reprocessing in editors

If you run the frame through the converter, it can rewrite the `ImageCount` field by inserting the export sequence number from Lightroom catalog.

Table of comparison of counting algorithms

Service type	Read tag	Result accuracy
Our online service	Direct binary subtract MakerNote 0x00A7	Absolute (100% accuracy)
Simple universal sites	Standard EXIF ​​ImageCount field	May confuse electronic and mechanical frames
Graphic editors	Export serial number in the catalog	Low (shows file number)