Thats the way to do it. Except I do the walkin myself. After 2 reels its nap time.
I have 2 spots marked on my driveway that are exactly 100 foot apart I stand with rod tip at one spot and send my son to the other spot with filler spool if my line counters don't say 100 I reel up then add or subtract more line from filler spool and send son out again to the 100 foot mark until every reel says 100 this way may take some time but its pretty much spot on with no issues yet
wilbur LIKED above post
And you can always use the "math" method : if line is trailing at 45deg angle, multiply length of line out by 0.6 & you will have the approx. depth of your weight/bait. Or in other words, every foot of length of line out (& below the surface of the water) will equal 7.2 inches of depth (IF line is at 45deg angle). Or in other words :
40 x 7.2 = 288 divided by 12 = 24
With a known 40ft of line out, depth is 8ft for every 15deg of angle :
15deg = 8ft
30deg = 16ft
45deg = 24ft
60deg = 32ft
90deg = 40ft
And since depth is measured by length of line BELOW the water's surface, & NOT distance from rod tip to bait, you have to factor in any length of line from rod tip to water's surface and subtract that length of line from your total length of line out.
So if you have 40ft of line out, and the line from rod tip to water is 4ft long, you'd use 36ft as your "distance". Then at a 45deg angle, 36ft of line would equal a depth of about 21.5ft deep for your bait. (36 x 0.6 = 21.6)
The hardest part of all this is figuring out at what angle your line is running
... cp