The dataset ranks 31 companies, and filing is highly concentrated: the top 5 assignees together hold 75.9% of all 108 records in scope, with the single leading assignee alone accounting for 41 filings. The gap to the fifth-ranked assignee, which holds 4 records, is large, meaning one company’s portfolio effectively defines the baseline prior art most new filers must design around. Beyond the top 10, which combine for 88.9% of records, the remaining assignees each hold small, often single-digit counts, forming a long tail typical of a mature measurement-technology field.

Filings rose from 4 in 2017 to a peak of 27 in 2020, then declined sharply, with the 2021-to-2024 span showing a -100% change. However, publication typically lags actual filing by around 18 months, so the 2025 and 2026 figures in any dataset are still incomplete and should not be read as a firm decline. Taken together, the pattern looks like a cooling off from an unusually active 2020 rather than an emerging trend, but it is too early to call the field closed.

The overwhelming majority, 90.7% of the 108 records in scope, fall under IPC class G01F, which covers flow, level and volume measuring instruments. A smaller but notable share, 11.1%, also touches G01P (velocity and acceleration measurement), and several other classes — including G01N material analysis, H04M telephonic communication, and container-related classes — appear in low single-digit shares. This tells you calibration innovation is happening mostly inside the core measurement discipline, with only thin activity spilling into adjacent fields.