Psalter/Bible/Prayerbook Organs
Psalters are a good source for researching organ history as there are almost no archaeological specimens of organs from the 7th century CE to the 14th century CE
The organ representations in the Psalter often do not correspond to a playable variant, but provide information about the technical status of organ development.
The representations are usually to be interpreted in a religious context and often only correspond to wishful thinking.
Nevertheless an excellent source for organ research.