update some language for algorithm overview

Author: marionbarker

docs/operation/algorithm/overview.md

@@ -1,11 +1,16 @@
 ## Loop Algorithm
 
-Loop’s algorithm for adjusting insulin delivery is oriented around making a blood glucose prediction. Every five minutes, triggered by new blood glucose data, it generates a new prediction. Both [bolus recommendations](bolus.md) and [temporary basal rate adjustments](temp-basal.md) are set based on this [prediction](prediction.md).
+Loop’s algorithm for adjusting insulin delivery is oriented around making a blood glucose prediction and modifying delivery to bring that prediction within target range without going below the Glucose Safety Limit. Every five minutes, triggered by new blood glucose data, it generates a new prediction. Both [bolus recommendations](bolus.md) and [temporary basal rate adjustments](temp-basal.md) are set based on this [prediction](prediction.md).
+
+!!! abstract "Glucose Prediction"
+    The *prediction* is a calculation based on the known parameters of current and historical glucose values, current and historical insulin delivery using any entered carbs. Loop's model predictive control (MPC) calculation includes the user's therapy settings modified by active overrides. This calculation is updated at the next glucose reading and the recommended insulin delivery may be updated.
+
+    The predicted glucose shown assumes no changes to future insulin delivery, when in fact, the insulin delivery is likely to be modified based on actual glucose. In that sense, the glucose prediction shown in various charts in the *Loop* app are meant to communicate the reason for the current dosing from *Loop*. Especially in the case of very low or very high *predictions*, be assured that *Loop* will attempt to change dosing to prevent that future glucose from happening, while keeping the user above the Glucose Safety Limit.
 
 ## Algorithm Terminology
 
 This graph and legend illustrates terms commonly used in discussing Loop's algorithm,
-and shows them in the context of historical and forecasted blood glucose in style similar to the
+and shows them in the context of historical and predicted blood glucose in style similar to the
 status screen of Loop.
 
 ![Chart illustrating terms](img/terms_graph.png)
@@ -21,7 +26,7 @@ status screen of Loop.
 |Eventual blood glucose|The last value of the predicted glucose curve, in other words the very last blood glucose predicted at the end of your insulin action duration. In the figure above, this is 85 mg/dL.|
 |Minimum predicted blood glucose|The lowest blood glucose value at any point in time within the prediction. In the figure above, this is 77 mg/dL.|
 |Delta|The delta is the difference between the eventual blood glucose and the correction target. In the overview figure, the eventual blood glucose is 85 mg/dL and the correction target is 105 mg/dL, which means that the delta is  -20 mg/dL. |
-|Suspend Threshold|The suspend threshold is a safety feature of the Loop algorithm. If any predicted blood glucose is below this threshold, the Loop algorithm will issue a temporary basal rate of 0|
+|Suspend Threshold (Glucose Safety Limit)|The glucose safety limit (called suspend threshold when this figure was generated) is a safety feature of the Loop algorithm. If any predicted blood glucose is below this value, the Loop algorithm will issue a temporary basal rate of 0|
 |CGM data|Blood glucose readings made by a continuous glucose monitor.|
 |Insulin sensitivity factor|A configuration value that provides an estimate of how much blood glucose will drop given a unit of insulin.|
 |Active insulin|Active insulin, often referred to as Insulin-on-Board (IOB), is the remaining amount of insulin activity from boluses and temporary basal rates relative to a user’s scheduled basal rates. More specifically, it is the total amount of insulin activity due to all bolus and basal insulin delivered within the last N hours, where N is determined by the insulin activity duration. The amount of “active” insulin depends upon the insulin activity curve, and also accounts for the insulin withheld via basal suspensions. As such, it is possible that the active insulin can be negative. Negative active insulin will result in an increase in predicted blood glucose. The active insulin displayed in Loop's main display does not reflect the currently enacted temporary basal rate, as that basal rate may be canceled or modified before completion over the next 30 minutes. In others words, Loop doesn't count chickens before the eggs hatch...insulin delivery must be confirmed before being added to the active insulin reporting.|