diff --git a/qpms/tolerances.h b/qpms/tolerances.h
index e3259a9..48e0a13 100644
--- a/qpms/tolerances.h
+++ b/qpms/tolerances.h
@@ -2,9 +2,14 @@
 #ifndef QPMS_TOLERANCES_H
 #define QPMS_TOLERANCES_H
 
+// TODO DOC
+
 typedef struct qpms_tolerance_spec_t {
 	double atol;
 	double rtol;
 } qpms_tolerance_spec_t;
 
+/// A rather arbitrary default tolerance.
+static const qpms_tolerance_spec_t QPMS_TOLERANCE_DEFAULT = {.atol = 1e-15, .rtol =  1e-8};
+
 #endif // QPMS_TOLERANCES_H