The statistics show whether a History difference in a given Level is in pre-defined of -10 to +10, above that range or below that range. The value range is adjustable in application options under menu Tools - Options - History - Ranges. The default values are -10 to +10.
Value "in range" means that the History difference value is in pre-defined range. Value ">" means the difference is above the pre-defined range, value "<" means the differences is below the pre-defined range.
These statistics are available in summary form and also as per-ticket properties.
See also In Range Differences statistics.