What is instability index (IUS)?

Instability index, abbreviated as I_US  is a quantitative analysis result based on the following calculation formula, which accumulates the signal variation between two consecutive scans. Each sample scanning provides a newly calculated I_US. Therefore, a change curve of instability index can be generated once the measurement is completed. The stability of the samples can be quantitatively evaluated and compared based on their values of I_US and variation trends.