Name: Cardio Drift Graph
Author: momoTM

Cardio Drift Graph data field app calculates cardiovascular drift as percentage change between pace and heart rate ratio (PaHR-%) in the first and second half of the workout at the current time. Data field value is updated once a minute and calculations are done only when the timer is on. So this is an almost real time PaHR calculator of your cardiovascular fitness, dehydration and energy level. Aerobic cardio workout target value is said to be +5% or below but can vary greatly due to various environmental and individual factors. Just google with words "cardiac drift", "aerobic decoupling" and "cardiovascular drift" to find out more.
Only PaHR-% values between -10 and +20 are shown in the graph because they are most important and that makes it easier to read. The colour of the graph is blue if the latest value is less or equal to +5 and red for over it. The data of the graph is saved and can be seen on Garmin Connect. There are also values for pace and heart rate in the upper part of the field. Pace is calculated as an avg pace of 8 seconds and current heart rate is shown on every 8th second. Pace is displayed in min/km or min/mil depending on the selected system units of the device.
Cardio Drift Graph app data draws a nice graph for those every one minute data values on watch screen and Garmin Connect web site so that you can see the history of those values and how they have changed during your workout. Every value is calculated for the first and second half of the duration time of the workout. In the beginning of the workout like warming up you normally see great variation of the values as a normal sign of physiological cardiovascular response but after that over time you begin to see some upward drift of the values especially with constant pace. You may see negative values as a sign of negative drift, too.
You may install this data field as any other data field app. Using it is easy. Just press Start button to start your workout and you will see values for pace, hr after 8 secs and PaHR-% as soon as there are values between -10 and +20. After that PaHR-% data field is updated once a minute and saved in your workout data file.
The code is based on work from babysimon_uk: https://apps.garmin.com/en-US/developer/f903f839-93ad-40f4-9a44-0efdaa1b7812/apps

PwHR (power/heart rate ratio) version of this app will be released this fall.

Enjoy!