I just flew from the top of a large hill down to the Gatineau river and the height measument dropped as I descended down the hill to the rivers edge.  I expected that it would but it maxed out at minus 7 (-7) metres.  Is that the max the drone height will show if descending below the take off height or an error in my drone ?

I would have thought it should show 'greater' negative numbers than that,
You might like to have a look at https://forum.dji.com/forum.php?mod=viewthread&tid=309158 and the Phantomhelp replay on it, it's still alive, not a mini 3 pro but ........
I have several mini 3 pro logs in my library that go appreciably lower than that, I just want to check the lowest before posting their low point just incase it was a malfunctioning drone.
The lowest I have found that is sensible is -394ft.

No ... there's no maximum negative height that can be displayed.

Hi there. It should show the negative height. Please fly cautiously as flying down buildings or valleys may weaken transmission and GPS signals. Have a nice day.

Labroides Posted at 4-5 13:29
No ... there's no maximum negative height that can be displayed.

There is a limit.
There is also a maximum positive height, which becomes negative after a certain value. This is a high altitude, several kilometers.

Serg SSA Posted at 4-8 02:55
There is a limit.
There is also a maximum positive height, which becomes negative after a certain value. This is a high altitude, several kilometers.

There is a limit.
If there is, it's a long way down.
I've seen a lot of large negative heights and not seen anyone who's hit a limit yet.

There is also a maximum positive height, which becomes negative after a certain value.
????

Labroides Posted at 4-8 03:39
There is a limit.
If there is, it's a long way down.
I've seen a lot of large negative heights and not seen anyone who's hit a limit yet.

3300m, then -3300 and tends to zero.

Drone.Hunter Posted at 4-8 05:45
3300m, then -3300 and tends to zero.

If you are going to 3300 metres, that drone has been hacked.
The OP wasn't asking about hacked drones and will never see that (like almost every other member here).

Labroides Posted at 4-8 03:39
There is a limit.
If there is, it's a long way down.
I've seen a lot of large negative heights and not seen anyone who's hit a limit yet.

You can request an official altitude unlock from DJI in the same way as the NFZ unlock.
If you have altitude unlocked, you can go up several kilometers. After an altitude of 3277m, the value should start with a “-” sign and the altitude will decrease, while the drone rises upward.
I repeat, you can officially unlock the height.
I provided this information for information only as an example of the fact that there are limitations in the indications)

Serg SSA Posted at 4-8 07:24
You can request an official altitude unlock from DJI in the same way as the NFZ unlock.
If you have altitude unlocked, you can go up several kilometers. After an altitude of 3277m, the value should start with a “-” sign and the altitude will decrease, while the drone rises upward.
I repeat, you can officially unlock the height.

But that's completely irrelevant to the OP's question.
Almost no-one will ever experience this.

Labroides Posted at 4-8 07:29
But that's completely irrelevant to the OP's question.
Almost no-one will ever experience this.

This is true, but I didn’t answer the person who asked the question, but you, because you stated that there are no maximum values in the readings. I provided information that the maximum values in the program readings are 3277 m.
No ... there's no maximum negative height that can be displayed.

Serg SSA Posted at 4-8 07:39
This is true, but I didn’t answer the person who asked the question, but you, because you stated that there are no maximum values in the readings. I provided information that the maximum values in the program readings are 3277 m.
No ... there's no maximum negative height that can be displayed.

And there is none for his drone and almost everyone else's

Labroides Posted at 4-8 07:51
And there is none for his drone and almost everyone else's

I have provided information, if you think that the knowledge is unnecessary, do not use it. Maybe someone will find it interesting. What is the problem?