dimentioning an arc gives un consisten results

iv been dimentioning a arc  and the anser it gives me is not consistent 

i have atached a video whre u can see i dimention the arc 4 times getig 1 anser 2 times and the uther anser 2 times uil cee in the video i click the same point evry time

cant upload file not to wory  hear's a youtube link

video link not showing search    

arc dimension inconsistent AS2014

Hi Alick

If you would like to send me your model at support@graitec.co.uk I'll take a look at it and see what's happening. Unfortunately it is difficult to see exactly where you are snapping to in the video.

Regards

Graitec Support

Hi Alick,

 To create a  dimension on a curved beam:

1. Select the Arc icon located on the Labels and Dimensions tab

2. Choose the arc tool on the Parametric dimensions panel

3. Select the arc then type “3p” then enter

4. Select the left endpoint of the arc using the node snap then the right end using node

5. Select the midpoint of the circle using the nearest snap mode

6. Now select the right endpoint of the arc using the node snap then the left end using node

7. Your Radial dimension is displayed automatically
   

I hope this helps

Regards,

hi Janet Black your instructions worked thanks

dont know y it worked this time last time i triyed to use the 3p  methid  it keps saying Circle centre point (3P/2P/Radius) as if i hadent ask it to change to 3p  

oh well working now  thanks