diff --git a/README-json.md b/README-json.md
index e12891e..3a5e10b 100644
--- a/README-json.md
+++ b/README-json.md
@@ -37,9 +37,10 @@ This file contains dump1090's list of recently seen aircraft. The keys are:
  * now: the time this file was generated, in seconds since Jan 1 1970 00:00:00 GMT (the Unix epoch).
  * messages: the total number of Mode S messages processed since dump1090 started.
  * aircraft: an array of JSON objects, one per known aircraft. Each aircraft has the following keys. Keys will be omitted if data is not available.
-   * hex: the 24-bit ICAO identifier of the aircraft, as 6 hex digits. The identifier may start with '~', this means that the address is a non-ICAO address (e.g. from TIS-B).
-   * type: 
-   * flight: the flight name / callsign
+   * hex: the 24-bit ICAO identifier of the aircraft, as 6 hex digits. 
+       The identifier may start with '~', this means that the address is a non-ICAO address (e.g. from TIS-B).
+   * type: type of the modeS address e.g. ADS-B, ADR-R, TIS-B
+   * flight: callsign, the flight name or aircraft registration as 8 chars (2.2.8.2.6)
    * alt_baro: the aircraft barometric altitude in either feet or meters
    * alt_geom: geometric (GNSS / INS) altitude in either feet or meters
    * gs: ground speed in knots
@@ -53,30 +54,36 @@ This file contains dump1090's list of recently seen aircraft. The keys are:
    * true_heading: Heading, degrees clockwise from true north
    * baro_rate: Rate of change of barometric altitude, feet/minute
    * geom_rate: Rate of change of geometric (GNSS / INS) altitude, feet/minute
-   * squawk: identity (Squawk), encoded as 4 hex digits
+   * squawk: Mode A code (Squawk), encoded as 4 octal digits, useful for ADS-B report correlation with SSR data
    * emergency: provide asdditional information regarding aircraft status (2.2.3.2.7.8.1.1)
    * category: emitter category to identify particular aircraft or vehicle types (values A0 - D7) (2.2.3.2.5.2)
-     - Set A: Light, Small, Large, High Vortex Large, High Performance, Rotorcraft
-     - Set B: Glider, Lighter than Air, Parachutist, Ultralight, Unmanned Areal Vehicel, Space/Transatmospheric vehicle
-     - Set C: Emergency Vehicle, Service Vehicle, Obstruction
+     - Set A: 
+         1 Light, 2 Small, 3 Large, 4 High Vortex Large, 5 Heavy, 6 High Performance, 7 Rotorcraft
+     - Set B: 
+         1 Glider,2 Lighter than Air, 3 Parachutist, 4 Ultralight, 6 Unmanned Areal Vehicel, 7 Space/Transatmospheric vehicle
+     - Set C: 
+         1 Emergency Vehicle, 2 Service Vehicle, 3..5 Obstruction
      - Set D: Reserved
    * nav_qnh: altimeter setting (QFE or QNH/QNE), millibars
    * nav_altitude: selected altitude
    * nav_heading: selected heading
-   * nav_modes: ['autopilot', 'vnav', 'althold', 'approach', 'lnav', 'tcas']
+   * nav_modes: target state and status with 'autopilot', 'vnav', 'althold', 'approach', 'lnav', 'tcas'
    * lat, lon: the aircraft position in decimal degrees
    * nic: Navigation Integrity Category (2.2.3.2.7.2.6)
-   * rc: Radius of Containment in meters 
+   * rc: Radius of Containment, (Rc) 
+       is the radius that there is a 95% probability the aircraft is within that radius of its stated position, 
+      both horizontally and vertically. 
    * seen_pos: how long ago (in seconds before "now") the position was last updated
    * version: ADS-B Version Number 0, 1, 2 (3-7 are reserved) (2.2.3.2.7.5)
    * nic_baro: Navigation Integrity Category for Barometric Altitude (2.2.5.1.35)
    * nac_p: Navigation Accuracy for Position (2.2.5.1.35)
    * nac_v: Navigation Accuracy for Velocity (2.2.5.1.19)
    * sil: Source Integity Level (2.2.5.1.40)
+       probability of the reported horizontal position exceeding the radius of containment defined by the NIC
    * sil_type: unknown, perHour, perSample
    * gva: Geometric Vertical Accuracy  (2.2.3.2.7.2.8)
    * sda: System Design Assurance (2.2.3.2.7.2.4.6)
-   * mlat: list of fields based on MLAT e.g. ['lat', 'lon', 'nic', 'rc', 'nac_v']
+   * mlat: list of fields based on MLAT e.g. 'lat', 'lon', 'nic', 'rc', 'nac_v'
    * tisb: ??? list of fields based on TIS-B ???
    * messages: total number of Mode S messages received from this aircraft
    * seen: how long ago (in seconds before "now") a message was last received from this aircraft