The long is substituted in kram before a śit affix, in the parasmaipada ,
As क्रामति, क्रामतः, क्रमन्ति ॥ Why in the Parasmaipada? Observe आक्रमते आदित्यः ॥ How do you explain the lengthening in उत्क्राम and संक्राम (Imperative 2nd Person Singular)? For when हि is elided by लुक्, 6.4.105 then by 1.1.63, the affix being dropped by a लु-elision, it would produce no effect and so there ought to have been no lengthening? This is no valid objection. The prohibition of (l. I. 63), applies to the अङ्ग stem after which the affix is elided. Here क्रम् is not a stem or anga with regard to हि, but it is a stem with regard to शप्, as क्रम् + शप् + हि ॥ Therefore, though हि is elided, the lengthening will take place by 1.1.62, (प्रत्यय लक्षणम्) ॥,