A20 manafold guage doesn't increase with wep, engine sound does, external veiw u can see instument panel,compass flickers, gunsight wobbles.
262: on right wing where flap joins there is odd discoloration,cann see thru part of right aileron, see insturment panel thru plane
P51D: see thru wings see cockpit thru plane
Tempest: without wep boost guage is below 0 with wep it is at 0
niki: when carrying bombs can only see left one when dropping them u can see both