“Devsur Samachari” does not mean a specific granth like Kalpasutra or Pravachansar. It is the particular way (samachari = practice / conduct / method) followed in the Tapāgaccha, mainly about tithi‑calculation and related rituals.

Origin in short

• In later centuries (around 17th–18th century Vikram period), within the Śvetāmbara Tapāgaccha there arose a dispute about how to count tithis (lunar dates) for festivals and rituals – this is called “Tithi Vivād”.
• After Acharya Vijayānsurī, two lines were spoken of:

- Ansur Tapāgaccha - Devsur Tapāgaccha (named from Acharya Vijaydevsuri / Devsuri).

• The main difference between these two was how to accept the 13th tithi when the first day is omitted.
• In time, the two lines re‑united, but the tithi‑practice of the Devsur line became the accepted standard in Tapāgaccha.
• Because of this, the present Tapāgaccha practice in such matters is called:

- “Devsur Samachari” - “Devsur Tapāgaccha Sangh”, etc.

So:

• “Devsur Samachari” = the traditional Tapāgaccha way of observing tithis and connected achar, based on the lineage and decisions of Acharya Devsuri (Vijaydevsuri) and his paramparā.
• It is within Śvetāmbara Tapāgaccha only; Digambar tradition does not use this term.