As a general rule you will want to use a mid-to-high dpi for engraving text or other items with fine details, and a lower dpi for photographs or large block-style objects. Again this is a general rule and you should experiment with the different settings to understand the different results you can achieve. The higher the dpi the more dots the laser will mark (basically more details) however this also increases the overall marking time. A lower dpi will provide for faster marking times but is not suitable for all jobs. One thing to keep in mind is that the lower the dpi you use the more laser power will be required in order to achieve the same depth/darkness of mark.