Quick intro reference for the Sense Home Energy Monitor thus far undocumented API. This was taken from the Sense Android app version 1.3.7-9be446d, which was available in Google Play store on February 6th, 2017.

quick_sense_API_ref.txt

-- Authentication --
URL: https://api.sense.com/apiservice/api/v1/authenticate
Method: POST
Fields:
  email (your email)
  password (your password)


response JSON:
{
    "authorized": true,
    "account_id": NNN1,
    "user_id": NNN2,
    "access_token": "t1.4335.4330.blahblah",
    "monitors": [{
        "id": NNNN,
        "time_zone": "America/New_York",
        "solar_connected": false,
        "solar_configured": false
    }],
    "bridge_server": "wss://mb1.home.sense.com"
}


-- Device list --
Example: https://api.sense.com/apiservice/api/v1/app/monitors/NNNN/devices

URL: https://api.sense.com/apiservice/api/v1/app/monitors/NNNN/devices
Method: Get

response JSON: (groups of)
[{
	"id": "HEXXXXX",
	"name": "Unnamed motor 2",
	"icon": "UnknownMotor",
	"tags": {
		"Alertable": "true",
		"DeviceListAllowed": "true",
		"Mature": "true",
		"name_useredit": "false",
		"OriginalName": "Unnamed motor 2",
		"Revoked": "false",
		"TimelineAllowed": "true",
		"TimelineDefault": "true",
		"Type": "UnknownMotor",
		"user_editable": "true"
	},
	"type": "UnknownMotor"
}]


-- Sense monitor (the actual Sense device) status --
Example: https://api.sense.com/apiservice/api/v1/app/monitors/NNNN/status

URL: https://api.sense.com/apiservice/api/v1/app/monitors/NNNN/status
Method: GET

resposne JSON:
{
	"signals": {
		"progress": 100,
		"status": "OK"
	},
	"device_detection": {
		"in_progress": [],
		"found": [{
			"icon": "Microwave",
			"name": "Microwave",
			"progress": 70
		}],
		"num_detected": 8
	},
	"monitor_info": {
		"serial": "M649XXXXXX",
		"online": true,
		"version": "1.1.1379-d95b692-master",
		"ssid": "WifiNetworkSSID",
		"signal": "-29 dBm",
		"mac": "a4:d5:xx:xx:xx:xx"
	}
}


-- Get usage history --
Example: https://api.sense.com/apiservice/api/v1/app/history/usage?monitor_id=NNNN&granularity=SECOND&start=2017-02-07T01:48:00.000Z&frames=5400

URL: https://api.sense.com/apiservice/api/v1/app/history/usage
Method: GET
fields:
  monitor_id (the "id" returned by authenticate)
  granularity (timespan unit [acceptable values: SECOND, MINUTE, ???])
  start (start time of data in UTC [like 2017-02-07T01:48:00.000Z])
  frames (how many data samples you will retreive [default is 5400])


response JSON:
{
    "totals": [
        [279, 279],
        [279, 279],
        [279, 279],
        ..... (many more samples of data)
    [1, -1],
        [1, -1],
        [1, -1]
    ],
  "endOfData": "2017-02-07T02:57:26.000Z",
    "start": "2017-02-07T01:48:00.000Z"
}


-- Get trend data --
Example: https://api.sense.com/apiservice/api/v1/app/history/trends?monitor_id=NNNN&scale=WEEK&start=2017-01-30T05:00:00.000Z&read_combined=false

URL: https://api.sense.com/apiservice/api/v1/app/history/trends
Method: Get
fields:
  monitor_id (the "id" returned by authenticate)
  scale (the bin for data [accepatble values: DAY, WEEK, MONTH, YEAR]
  start (start time of data in UTC [like 2017-01-30T05:00:00.000Z]
  read_combined


response JSON: (note that many devices are contained within the ../consumption/devices node)
{
	"steps": 28,
	"start": "2017-02-01T05:00:00.000Z",
	"end": "2017-03-01T05:00:00.000Z",
	"consumption": {
		"total": 51.398094,
		"totals": [10.689455, 10.410812, 10.78235, 9.346396, 10.169082, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0],
		"devices": [{
			"id": "8cb442c4",
			"name": "Bathroom Light Incandescent ",
			"make": "",
			"location": "",
			"icon": "Lighting",
			"tags": {
				"Alertable": "true",
				"DeviceListAllowed": "true",
				"Mature": "true",
				"name_useredit": "true",
				"OriginalName": "Light 1",
				"Revoked": "false",
				"TimelineAllowed": "true",
				"TimelineDefault": "true",
				"Type": "Lighting",
				"user_editable": "true"
			},
			"history": [0.03463329, 0.052048903, 0.13162036, 0.045925356, 0.1306975, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0],
			"type": "Lighting",
			"avgw": 0.014104479,
			"pct": 0.76836586
		}
	},
	"production": {
		"total": 0.0
	},
	"scale": "month"
}

-- Real time data feed --
This is a websocket conversation that updates data multiple times a second.

use "monitor" from authentication:
URL: wss://mb1.home.sense.com/monitors/NNNN/realtimefeed

response websocket data example:
Type: binary
start/end: provided
message: HEXY MCHEXFACE

I missed the notice for your comment. I assume that it's simply a Y-value on a graph as rendered in the UI.