Ok, maybe I found the answer.
So I found a table with following values
Segment SampleRTT EstimatedRTT DevRTT Time Out
1 130 130.00 130.00 650.00
2 138 131.00 99.25 528.00
3 122 129.88 76.41 435.50
4 124 129.14 58.59 363.50
5 131 129.37 44.35 306.77
Looks like EstimateRTT, DevRTT have at first the same value as the sampleRTT(130).
The rest can be calculated with following formula as
b = 0.25; a = 0.125
EstimatedRTT = (1- a)EstimatedRTTlast + aSampleRTT
DevRTT = (1-b)DevRTTlast +b|SampleRTT-EstimatedRTT|
Timeout = Estimated RTT + 4*DevRTT
Source: https://www.ukessays.com/essays/it-research/round-trip-time-rtt.php
Update:
Ok, thanks to Zac I was looking in RFC 6298
Where it says:
(2.2) When the first RTT measurement R is made, the host MUST set
SRTT <- R
RTTVAR <- R/2
RTO <- SRTT + max (G, K*RTTVAR)
where K = 4.
So in first Segment EstimatedRTT=SampleRTT, DevRTT=SampleRTT/2.
So the table would look in the first segment like this, if I understood it right:
Segment SampleRTT EstimatedRTT DevRTT Time Out
1 130 130.00 65.00 390.00
Now which source should I rather trust ? I think the RFC 6298