Gauge indicator help

[UpstateSC]

Hey Gang,
Being pretty much brand new to Tesla and our Model S I was hoping someone could help clarify what this gauge indicates for the car? I saw it somewhere in the manual and it seemed to mention limiting acceleration, but I'm still unclear why it shows up from time to time and what exactly it indicates.
Sorry if it's been discussed at length. I couldn't figure out a good way to search since I wasn't sure what the gauge was called. Thanks for any input.

 

[UpstateSC]

Forgot the picture.

 

[Tam]

...what exactly it indicates...

You can go to your central screen to expand that red triangle icon to see its message.

 

[DerbyDave]

On the Energy graph, dashed lines appear on the power meter if Model S is limiting power.
The dashed lines appear on the top portion (energy being used) when power available for
acceleration is being limited, and on the bottom portion (energy being gained) when power
that can be gained by regenerative braking is limited. Model S limits power for many reasons.
Here are just a few examples:
• Acceleration may be limited when the Battery is reaching a low state of charge or if the
powertrain is hot.
• Both acceleration and regenerative braking may be limited when the ambient temperature
is either very high or very low.

The Energy app displays real-time feedback
on the amount of energy being gained by
regenerative braking. You can also display the
power meter on either side of the instrument
panel by choosing Energy using the scroll
button on the steering wheel (see Steering
Wheel on page 44).
The amount of energy fed back to the Battery
using regenerative braking can depend on the
current state of the Battery and the charge
level setting that you are using. For example,
regenerative braking may be limited if the
Battery is already fully charged or if the
ambient temperature is too cold.
Note: If regenerative braking is limited, a
dashed yellow line displays on the power
meter.

A Yellow Triangle with an Exclamation mark in it may appear from time to time. This is to alert you that either regenerative braking levels, or power levels have changed, and thus a change in driving power or braking has occurred. This will enable you to change your driving to reflect the change.