I am not quite sure about the pattern of sentence "My watch is running slow" ? Is it a SVOC or something ? Would anyone explain it in detail ?
SUBJECT (“My watch”) plus intransitive VERB in present progressive tense (“is running”) plus ADVERB (“slow,” despite the lack of -ly suffix, which if present would alter the adverb’s meaning but not its part of speech—see below). It is the same basic sentence pattern as “He is sleeping soundly.”
A timepiece running at the exactly correct speed, but set so that it consistently indicates a time later than the relevant standard, is running slow but not slowly. Some people deliberately set inherently and otherwise accurate car-dashboard clocks and wristwatches fast in the usually vain hope that it will improve their own punctuality.