3min power reflects what Focus Type you have currently selected for the program you are on.
For example, I only see 4 min when I hover over the circles because I have Puncheur selected for my Continuous program.
Double tap on a circle to view details for that BT including Focus for that activity.
Size and color of the circles provides at-a-glance info about the BT –
What do the coloured circles on my XPMC mean? – Xert
Something interesting you can do with a BT activity is click on the Previous button below the chart to show MPA drawdown with your prior signature applied. You can then zoom in on the BT segments and see how long you exceeded MPA and by how much. If there was more than one BT detected Xert adjusts your signature so only one point touches the MPA line.
Tip for the future –
There will be times you generate a BT that you don’t want applied. For example, an abrupt stop at the line may generate a BT but you didn’t fail naturally and you could have kept going. Or you may have power spikes in the data which Xert attempts to filter out during analysis but one snuck by and bumped your signature. Or you got a Near BT which slightly lowers signature values and you prefer not to do that. Its not necessarily a bad thing as it improves your chances to generate a BT in the future but many hate to see any decline while they’re training. 
For these situations you can flag the activity which retains the strain score for TL purposes but skips signature calculation.
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