I had a 318 block sonic tested and when it spilt 3 bores I measured the busted parts and none of them were what he told me, not even close so watch it done if possible and listen to what p body said, a chain is only as strong as it's weakest link or in other words a cylinder is only as strong as it's thinnest point.

I use to have a guy doing my sonic checking that
did 64 reading per cyl... charged $75 at that time..
he was well worth it... he was a old hard core guy
that did a lot of machine work also... very nice guy
and his prices on everything was on the cheap side compared
to most shops... I watched him do my mega block so I
knew he wasnt BSing on the numbers... guys that get a
small hand full of readings have no idea what the block
is really like... a 1/2" away it could be paper thin..
plus if he found a area that was iffy he would do a dozen
readings just in that area... no charge