answer to myself, it appears that the chep multimeter types with Current clamp, is only capable of measure AC current, I need also to measure DC current (Then I can measure if my my diesel glowplugs are working, without removing anything), so I bought this fairly cheap add on.
It provides 1mV/A
How to measure with current clamp your glowplugs: (Not my video, but it gave me some knowledge):
VW T4 Transporter -- Startprobleme: Vorglühanlage überprüfen – 11:40
— Sascha Supertramp