diff --git a/User-Registration-API.md b/User-Registration-API.md
index 5b71588..5eabd12 100644
--- a/User-Registration-API.md
+++ b/User-Registration-API.md
@@ -36,11 +36,35 @@ Where `year_of_birth` is between 10 and 150 years in the past.
   name : <organisation name>,
   street_name : <organisation street address>,
   town : <organisation village/town/city>,
+  sector : <sector area code>,
   postcode : <organisation postcode>,
   password : <password (used for login)>
 }
 ```
 
+Where the sector area code letter is based off the [ONS UK SIC 2007 classifications](https://www.ons.gov.uk/methodology/classificationsandstandards/ukstandardindustrialclassificationofeconomicactivities/uksic2007) shown here, which is broken down to the list below. 
+
+* A for: Agriculture, Forestry & Fishing
+* B for: Mining & Quarrying
+* C for: Manufacturing
+* D for: Electricity, Gas, Steam & Air Conditiioning
+* E for: Water & Waste Management
+* F for: Construction
+* G for: Wholesale & Retail Trade
+* H for: Transportation & Storage
+* I for: Accomodation & Food Services
+* J for: Information & Communication
+* K for: Financial & Insurance Activities
+* L for: Real Estate
+* M for: Professional, Scientfic & Technical
+* N for: Administrative & Support Services
+* O for: Public Administration, Defence & Social Security
+* P for: Education
+* Q for: Human Health & Social Work
+* R for: Arts, Entertainment & Recreation
+* S for: Other Service Activities
+* T for: Household Domestic Business
+
 ### Response JSON
 
 #### Success