Property plane just means a vertical extension of property lines .... all the lines. The Code doesn’t say take readings at the street, in fact it talks about not suffering specific noise levels AT ANY POINT outside the property plane.

"Property plane" means a vertical plane including the property line which determines the property
boundaries in space.

9.10.030 Residential property noise limits.
(a) No person shall produce, suffer or allow to be produced by any machine, animal or device, or any
combination of same, on residential property, a noise level more than six dB above the local ambient AT ANY POINT
outside of the property plane.

Readings to determine whether there is a violation under 9.10.030(a) can and should be taken on your side of the fence (there’s almost always a fence on side and rear property lines in Palo Alto, and fence lines in these locations most often follow property lines) in the area of closest proximity to where the noise is being generated on the neighboring property.

HOWEVER, the provisions of 9.10.030 apply at night, outside the hours set forth under 9.10.060(a) which allows a higher noise levels. Readings under the general daytime exceptions of 9.10.060(a) are taken at 25 feet from source of the noise. In this case 25 feet from the power tool. Depending on lot size and where on the lot the equipment is being used, the reading might be taken on your neighbor’s property or on the lot you live on.

Read the code. Read it again. Trust your readings. But how about starting by having a conversation with your neighbor, and see if you can work out a solution.