<p>This study aimed at revealing the technologies involved and functions of indigenous calendar systems in West Sumba, Indonesia, through analyses of intercalation methods, inter-area synchronization methods, and the reality of time reckoning. I found that the observation of the solar cycle in a mountain-top village in Lamboya District played a determinative role in the intercalation and times of the Loli and Wanokaka Districts, which were synchronized to this cycle through the Podu and Pasola Rituals, respectively, in the Month of Bitterness and the Month of Sea Worms. In addition, the Loli District played a key role in the inter-area synchronization of the 'end of the year' beyond district boundaries, while the Lamboya and Wanokaka Districts cross-checked the existence or absence of a natural phenomenon: sea worm (nyale) swarming. People recognized the Month of Bitterness as predicting the coming of the rainy season and the period for preparing garden crops (e.g. maize and millet) and the Month of Sea Worms as the end of the peak of heavy rains and the start of the period for planting rice in paddy terraces. In conclusion, this study found that the indigenous calendar was not fixed in a form of 'cells' but was flexible based on certain solar, lunar, natural, and cultural signals. This is a simple technology and a non-conscious calendar but it is very adaptive to these people's subsistence and is potentially resilient to extreme weather events. </p>