The TNM classification calculator evaluates the stage of distal cholangiocarcinoma based on three specific criteria: tumor classification, lymph node classification, and metastasis classification, each with distinct options for assessment. 

The tumor classification describes the invasion depth or extent concerning the bile duct and surrounding areas:
- Tx: Primary tumor cannot be assessed.
- T0: No evidence of primary tumor.
- Tis: Carcinoma in situ/high-grade dysplasia.
- T1: Tumor invading bile duct wall with depth < 5 mm.
- T2: Tumor invading bile duct wall with depth 5-12 mm.
- T3: Tumor invading bile duct wall with depth > 12 mm.
- T4: Tumor invading critical arteries (celiac axis, superior mesenteric artery, and/or common hepatic artery).

The lymph node classification indicates regional lymph node involvement:
- Nx: Regional lymph nodes cannot be assessed.
- N0: No regional lymph node metastasis.
- N1: Metastasis in 1-3 regional lymph nodes.
- N2: Metastasis in 4 or more regional lymph nodes.

The metastasis classification checks for distant metastasis presence:
- M0: No distant metastasis.
- M1: Distant metastasis present.

The computation uses these classifications to determine the cancer stage, employing a set codified logic:

- Stage 0: Tis, N0, M0
- Stage I: T1, N0, M0
- Stage IIA: T2, N0, M0, or T1, N1, M0
- Stage IIB: T2, N1, M0, or T3, N0/N1, M0
- Stage IIIA: T1/T2/T3, N2, M0
- Stage IIIB: T4, any N, M0
- Stage IV: Any T (except T0), any N, M1

The TNM classification for distal cholangiocarcinoma is a clinical staging system developed by the American Joint Committee on Cancer (AJCC). It is designed for the stratification of patients with distal cholangiocarcinoma, a type of bile duct cancer, based on the extent of the tumor (T), the involvement of regional lymph nodes (N), and the presence of distant metastasis (M). 

The primary components of this classification system include the size and extent of the primary tumor (T), the number and location of affected lymph nodes (N), and the presence or absence of distant metastasis (M). Each of these components is assigned a numerical value, with higher numbers indicating more advanced disease. The T category is determined by the size of the primary tumor and its extent of invasion into surrounding tissues. The N category is determined by the number and location of regional lymph nodes involved. The M category is determined by the presence or absence of distant metastasis. 

The final TNM stage is determined by combining the T, N, and M categories. This stage provides a comprehensive assessment of disease progression and is crucial in guiding treatment decisions and predicting patient prognosis. The TNM classification for distal cholangiocarcinoma allows for a standardized comparison of patient populations and facilitates clinical research in this field.