Different foundation and stand size for 42" oven?

[alex.g]

Look:
Pompeii Oven | Dimensions

77" x 86" for foundation
69" x 76" for block stand

then open pompeii_oven_plans2.0.pdf
page 13

73" x 86" for foundation
65" x 78" for block stand

then open page 66
Material List 42" Oven

80" x 94" for foundation
72" x 84" for block stand


So.. where is the truth?
Thanks

[Tscarborough]

Interior oven size + 2x firebrick thickness + 2x insulation thickness + 2x house wall thickness(if used) = base size.

[alex.g]

it is ok, but why tree different demensions are mentioned?

[alex.g]

forgot.. when it is adviced to use 40cm (16") and 20cm (8") blocks (length), why no numbers with 8base, ok.. 72/8 is 9, but 84/8 is 10.5 halfbricks.