There is definitely no problem with negative results. The numerical value you mentioned only represents the data produced by the experiment. This data is only used to judge yin and yang. As long as it is negative, there is definitely no problem. The experiment itself will be influenced by many factors, and it is normal to fluctuate within a negative range. The reason why it is only used for qualitative purposes means that this value is not suitable for quantitative viewing. Don't worry, it is definitely no problem.