How should all fingers be pressed to obtain "plain" impressions?

To obtain "plain" impressions, pressing all fingers simultaneously is the correct approach. This technique ensures that the impressions are consistent and evenly spaced, which is crucial for identification purposes. When fingers are pressed down at the same time, it reduces the chances of smudging or misalignment that could occur if they were pressed individually or in succession. This method also captures the full detail of each fingertip, providing a more comprehensive and accurate representation of the fingerprint.

In contrast, pressing fingers one at a time or in quick succession may result in varying levels of pressure being applied. This can lead to distorted or incomplete impressions, making it harder to analyze the fingerprints effectively. Therefore, using simultaneous pressing is essential for achieving high-quality plain impressions that meet the necessary standards for identification and record-keeping.