Comprehensive and Detailed Explanation From Exact Extract:

Service Level Indicators (SLIs) provide the quantitative measurements needed to determine how much of the Service Level Objective (SLO) has been consumed. Since the error budget is defined as the allowable amount of unreliability, SLI data is the source of truth for calculating how much of that budget remains.

From the Site Reliability Engineering Book, Chapter ''Service Level Objectives'':

''SLIs provide the measurements used to determine compliance with SLOs. Error budgets are computed directly from the SLI measurements over the defined time window.''

The SRE Workbook further explains:

''Error budgets quantify the inverse of SLO performance. SLIs provide the raw data that allow teams to calculate how much of the budget has been consumed and how much remains.''

Thus, SLI data is the Only mechanism that determines remaining error budget.

Therefore, the statement is True.

Site Reliability Engineering Book, ''Service Level Objectives''

SRE Workbook, ''Implementing SLIs and SLOs''