HM8021 - Frequency counter

Version HM8021-1, discontinued

Version HM8021-2, discontinued

Version HM8021-3, discontinued
Datasheet as a PDF-file here

Version HM8021-4 (current version)

Internal view of HM8021-4
Data sheet for HM8021-4 as a PDF-file here
Service manual for HM8021-4 as a PDF-file here