I've used a similar version of the DIY reference for years and had good results.

I'm not sure about the string...

Unless the track width of both front and rear axles are identical, you introduce error. Specifically, most cars have a wider front track than rear track dimension. This induces a toe out error. Rear wheel drive cars require a toe in, not toe out.

Secondly, if I'm reading the method correctly, you cannot measure toe-in with the string method, because the line will continue to grip the front of the tire as you transition from toe out to toe in.

I'm not even going to go into the spreader bar..... You just have to account for tolerance stack up.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles