First Ultrasound heart rate?

Betsy
I had my first ultrasound yesterday.  I measured 5 wks 6 days.  And had a heartrate of 99. The tech and my doctor said that 99 is low?!!  Anyone else think that 99 is ok?  I've looked on Americanpregnancy.org and it appears the average is 90-110 for 5-6 wks.  Thoughts?