| Month | Subject | Author | Remark | |
| 05-01 | Babylonian and Italian hours (2) | Fer de Vries | ||
| 05-02 | Sundials topsy turvy | Thibaud Taudin Chabot | ||
| 05-03 | Sundial distribution over The Netherlands |
Thibaud Taudin Chabot | ||
| 05-04 | Decimal hours | Fer de Vries | ||
| 05-05 | New type of sundial Design Fred Sawyer |
Fer de Vries | Polar with hourlines each 15 degrees |
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| 05-06 | Constant daily insolation | Fer de Vries | ||
| 05-07 | Antique or unequal hours | Fer de Vries | ||
| 05-08 | Time system conversion 1 | Fer de Vries | ||
| 05-09 | Construction of a combination sundial |
Fer de Vries | ||
| 05-10 | Time system conversion 2 | Fer de Vries | ||
| 05-11 | Checking the Pattern | Fer de Vries | ||
| 05-12 | Bi-gnomon sundial Sundial for clock time |
Fer de Vries | Idea Hendrik Hollander | |