Bubs Heart Rate at 9 week ultrasound

[Rachett]

Can anyone tell me what their bubs heart was around the 9 week mark?
I have a friend who had a scan today, she's 9w2d along and bubbas heart rate was only 137bpm. She had a scan a week ago at 8w1d and the heart rate was 167bpm.
From what i understand the heart rate will peak around 9w and then will slowly start to drop, but this is a drop of over 30bpm in a week! Could this be a mistake by the ultrasound technician? or do the think the heart rate is perfectly fine?
My bubs heart rate at 8w4d was 174bpm and then at 10w4d 178bpm. Even now at almost 25 weeks it sits around 140bpm.
Appreciate all feedback, good or bad.
Thanks in advance.