If you are seeking effective ways to merge calendars in Outlook, then there is an informative article available that outlines a comprehensive guide on both manual and professional methods. The manual approach involves the following stages:

Stage 1: Export Items from the One Calendar
Stage 2: Import the Exported Items to the Desired Calendar

Alternatively, you can choose to use the Cigati PST Merger Tool, which is also featured in the article. This tool offers the advantage of merging multiple PST files into a single file while ensuring no data loss. It also enables the removal of duplicate emails and attachment files during the merging process. To evaluate its performance, users can opt to try its free demo version.