計數機點睇有無電？計數機腿色點算？

A non-dual powered calculator (such as the 3950P) usually has a much shorter runtime. In the case of old models, the only way to tell when battery replacement is necessary is to check if the LCD still displays solid characters, segmented digits etc. during operation. If the display starts to faint, then it's probably time to replace the battery.
However, in recent calculator models (especially those with dot matrix displays), some have low power warning function, which means if the calculator is running low on power then the "Low Batt" or similar message will be displayed, prompting the use to replace the battery immediately.
I am not sure if this is the case with the 3950P, I suggest you check the manual for details.

計算的字體越來越模糊，就是開始無電的現象。並且需要更換電池。