Final answer:
The temporary adjustments required in the prismatic compass are centering, levelling, and focusing the prism; adjustment of level is generally considered a permanent adjustment. Option 4 is the correct answer.
Step-by-step explanation:
The student asked which of the following are temporary adjustments required in the prismatic compass: 1) centering 2) levelling 3) focusing prism 4) adjustment of level. To answer this, it is essential to understand the prismatic compass, a device used in the field for navigation and for surveying to take bearings of distant objects.
To ensure accurate readings, several temporary adjustments need to be made:
- Centering - Ensuring that the compass is placed exactly over the survey station point.
- Levelling - The compass must be level to avoid parallax error; this means the bubble in the spirit level should be centered.
- Focusing Prism - Adjusting the prism ensures that the compass card and object in view are both seen clearly.
However, the 'adjustment of level' is typically viewed as a permanent adjustment rather than a temporary one. This involves setting the instrument such that the line of sight is horizontal when the bubble is centered.
Temporary adjustments are those that need to be made each time the instrument is used, to ensure accuracy. For the prismatic compass, correct operation typically involves centering, levelling, and focusing the prism. So, the correct options for temporary adjustments are 1) Centering, 2) Levelling, and 3) Focusing prism. Option 4, adjustment of level, generally falls under permanent adjustments.