The marks assigned in the NDA exam's Picture Perception and Description Test (PPDT) are based on various factors. Here is a general breakdown of how marks are assigned:

1. Content: The content of your description is crucial. Marks are given based on the relevance of the content to the picture, the logical sequence of events, and the ability to understand and interpret the situation depicted in the picture.

2. Organization: The organization of your description is also important. Marks are awarded for the ability to present your thoughts in a coherent and structured manner. It includes the introduction, body, and conclusion of your description.

3. Vocabulary and language skills: Your vocabulary and language skills are assessed. The use of appropriate words, sentence structure, and grammar are considered while assigning marks.

4. Originality: Marks are given for the originality of your description. It is important to provide a unique perspective and not simply repeat common ideas and phrases.

5. Communication skills: Your ability to effectively communicate your thoughts and ideas is evaluated. Marks are awarded for clarity, fluency, and coherence in your description.

6. Relevance to the given situation: Marks are assigned based on how well your description relates to the given picture and the situation it portrays.

7. Time management: The time allotted for the PPDT is limited, and marks are given for utilizing the time effectively. It is important to complete the description within the given time frame.

The overall performance in the PPDT is considered while assigning marks, and there is no fixed marking scheme as it may vary from examiner to examiner.