NEXCOM NPT 1550 - Manual (Page 14)

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3-3 Install VFD & MSR (Optional):
3-4-1 VFD install:
a. Unfasten the screws.
b. Install VFD Module on the rear cover.
c. Tighten the screws.
3-4-2 MSR install:
a. Unfasten the screws.
b. Pull the MSR cover from rear cover.
c. Install the MSR Module on the rear cover.
d. Tighten the screws.