Introduction:
When the sitting president of India is unable to discharge his functions due to illness or absence, the Constitution of India provides for the temporary transfer of powers and duties to either the vice president or the chief justice of India. In such cases, the vice president or chief justice performs the functions of the president until the president is able to resume his duties.

Explanation:
Here is a detailed explanation of how the temporary transfer of powers and duties takes place in the absence or illness of the president of India:

1. Oath of office:
When the vice president or chief justice of India is required to perform the functions of the president, they are not administered the oath of office of the president of India. They continue to hold their respective positions and perform the duties of the president in addition to their existing responsibilities.

2. Performing the functions of the president:
The vice president or chief justice of India, while discharging the duties of the president, does not physically occupy the office of the president. They continue to remain at their respective posts and exercise the powers and functions of the president as required.

3. Acting as the temporary president:
During the period when the vice president or chief justice of India is performing the functions of the president, they act as the temporary president. They make decisions, sign bills, and carry out other executive functions on behalf of the president.

4. Duration of temporary transfer:
The temporary transfer of powers and duties to the vice president or chief justice of India lasts only until the president is able to resume his duties. Once the president is capable of discharging his functions, the vice president or chief justice relinquishes their temporary role and the president resumes his normal duties.

Conclusion:
In cases where the sitting president of India is unable to discharge his functions due to illness or absence, the vice president or chief justice of India steps in to temporarily perform the functions of the president. They do not take the oath of office of the president but continue to hold their respective positions while exercising the powers and duties of the president. This temporary transfer of powers lasts until the president is able to resume his duties.