There is no simple answer to this question.
The answer depends on the region you are in and the standards you are working to. In China for example...

There is no simple answer to this question.
The answer depends on the region you are in and the standards you are working to. In China for example there are standardized correlation curves, which may be selected in the Original Schmidt Live app. Other regions such as Korea and Japan have nationally accepted correlation curves that are widely used. These may also be programmed directly into the Schmidt Live app and used. However, unless the standard you are using provides a method to use standardized curves then you should always calibrate your hammer to the concrete under test using a custom materials curve. If this is not possible we recommend using the lower 10th percentile curve with the Silver Schmidt OS8200 hammer to give a conservative estimate. This is a safer option with a smaller chance of overestimating the strength. Another option is to use the EN13791 screening test with either Original Schmidt OS8000 or Silver Schmidt OS8200 which again gives a conservative estimate. The use of custom material curves is fully explained in the tutorial "12. Custom materials" included in the Original Schmidt Live app.