diff --git a/owlps-positioner/cfg/owlps-positioner.conf b/owlps-positioner/cfg/owlps-positioner.conf
index 762ebaa..c663a07 100644
--- a/owlps-positioner/cfg/owlps-positioner.conf
+++ b/owlps-positioner/cfg/owlps-positioner.conf
@@ -93,6 +93,19 @@ csv-file = /tmp/owlps-positioner.log
 #area-start = -2;-2;0
 #area-stop = 20;30;6
 
+# Algorithm to calculate the similarity, in the signal strength space,
+# of two measurements.
+# The following algorithms are implemented:
+#   - mean: The mean of all the packets in the measurement is
+#     computed, then the euclidean distance between the two means is
+#     used.
+#   - interval: The mean Im and the standard deviation Is of the
+#     packets in the measurement I are computed; the closest reference
+#     measurement R is the one with the highest number of packets in
+#     the interval [Im-Is, Im+Is].
+# The default is "mean".
+#ss-similarity = mean
+
 # Smallest possible value for a received signal strength, in dBm. This
 # depends on the sensibility of the APs' Wi-Fi hardware. It is used to
 # compensate for APs that are not in coverage in a given measurement.
@@ -144,7 +157,7 @@ csv-file = /tmp/owlps-positioner.log
 # algorithm and derivated.
 
 # For a given positioning request, average all the calibration requests
-# associated with a reference point before to compute the SS distance.
+# associated with a reference point before to compute the SS similarity.
 # The default is false, i.e. the positioning request is compared
 # directly to each calibration request.
 #average-reference-points = false
diff --git a/owlps-positioner/src/measurement.cc b/owlps-positioner/src/measurement.cc
index 33c6002..e0145aa 100644
--- a/owlps-positioner/src/measurement.cc
+++ b/owlps-positioner/src/measurement.cc
@@ -7,6 +7,7 @@
 
 #include "measurement.hh"
 #include "posexcept.hh"
+#include "configuration.hh"
 
 #include <iostream>
 #include <sstream>
@@ -124,6 +125,35 @@ void Measurement::clear()
 /* *** Operations *** */
 
 
+float Measurement::similarity(const Measurement &source) const
+{
+  string algorithm(
+    Configuration::string_value("positioning.ss-similarity")) ;
+
+  if (algorithm == "mean")
+    return ss_square_distance(source) ;
+
+  if (algorithm == "interval")
+    {
+      float
+      interval_min = average_dbm - get_std_deviation(),
+      interval_max = average_dbm + get_std_deviation() ;
+
+      // Count the number of SS of source that are within the interval
+      unsigned int nb_values = 0 ;
+      for (map<pkt_id_t, ss_t>::const_iterator ss =
+             source.ss_list.begin() ; ss != source.ss_list.end() ; ++ss)
+        if (interval_min < ss->second && ss->second < interval_max)
+          ++nb_values ;
+
+      return 1 / nb_values ;
+    }
+
+  throw bad_configuration(
+    "Bad SS similarity algorithm name \""+ algorithm +"\"!") ;
+}
+
+
 void Measurement::recalculate_average()
 {
   average_dbm = 0 ;
diff --git a/owlps-positioner/src/measurement.hh b/owlps-positioner/src/measurement.hh
index 313a2ad..b6228f2 100644
--- a/owlps-positioner/src/measurement.hh
+++ b/owlps-positioner/src/measurement.hh
@@ -91,6 +91,8 @@ public:
 
   /** @name Operations */
   //@{
+  /// Computes the similarity with another Measurement in the SS space
+  float similarity(const Measurement &source) const ;
   /// Computes the distance to another Measurement's SS average
   float ss_square_distance(const Measurement &source) const ;
   /// Computes the distance to another SS value (in dBm)
diff --git a/owlps-positioner/src/posutil.cc b/owlps-positioner/src/posutil.cc
index 02b5ff4..d1ab16a 100644
--- a/owlps-positioner/src/posutil.cc
+++ b/owlps-positioner/src/posutil.cc
@@ -96,7 +96,7 @@ float PosUtil::ss_square_distance(
       unordered_map<string, Measurement>::const_iterator i2 =
         measurements2.find(i1->first) ;
       assert(i2 != measurements2.end()) ;
-      distance += i1->second.ss_square_distance(i2->second) ;
+      distance += i1->second.similarity(i2->second) ;
     }
 
   return distance / measurements1.size() ;
diff --git a/owlps-positioner/src/userinterface.cc b/owlps-positioner/src/userinterface.cc
index 542dd0e..c74ace8 100644
--- a/owlps-positioner/src/userinterface.cc
+++ b/owlps-positioner/src/userinterface.cc
@@ -26,6 +26,7 @@ namespace po = boost::program_options ;
   "/usr/local/etc/owlps/owlps-positioner.conf"
 
 /* Positioning options */
+#define DEFAULT_SS_SIMILARITY "mean"
 #define DEFAULT_MESHING_GRAIN 0.5
 #define DEFAULT_Z_MESHING_GRAIN 1
 #define DEFAULT_SMALLEST_SS -99
@@ -238,6 +239,10 @@ void UserInterface::fill_positioning_options()
   ("positioning.smallest-ss",
    po::value<int>()->default_value(DEFAULT_SMALLEST_SS),
    "Smallest possible value for a received signal strength, in dBm.")
+  ("positioning.ss-similarity",
+   po::value<string>()->default_value(DEFAULT_SS_SIMILARITY),
+   "Algorithm to calculate the similarity, in the signal strength space,"
+   " between two measurements. Allowed: mean, interval.")
   ("positioning.generate-reference-points",
    po::value<bool>()->default_value(false),
    "Generate reference points from the (auto)calibration requests"
@@ -280,7 +285,7 @@ void UserInterface::fill_positioning_options()
    po::value<bool>()->default_value(false),
    "With the NSS algorithm, for a given positioning request, average"
    " all the calibration requests associated with a reference point"
-   " before to compute the SS distance."
+   " before to compute the SS similarity."
    " The default is false, i.e the positioning request is compared"
    " directly to each calibration request.")
   ("positioning.nss.ignore-ap-reference-points",