Mechanical, low voltage and glazing takeoffs count different objects and follow one discipline. Count the things you buy, measure the things that run between them, and price labour as its own number rather than as a percentage of material. The products differ mainly in the libraries they ship, which is why an estimator moving between trades finds the software familiar and the labour units foreign.
Mechanical: equipment, then the distribution between it
Units, pumps, coils and terminals are counted; duct, pipe, insulation and hangers are measured. Mechanical takeoff software earns its keep on the distribution, because that is where the hours are and where a manual count of fittings takes an evening.
Low voltage estimating software: devices and the cable that reaches them
Low voltage estimating software counts cameras, access points, readers, panels and speakers, and then measures cable runs and terminations. The trap is the termination and test labour, which is invisible on the drawing and frequently exceeds the cable itself.
Glass quoting software: openings, sizes and the access to reach them
Glass quoting software prices by opening, with glass type, frame, hardware and seals, and then adds the access and handling that a large pane forces. Two openings of the same area can differ in price by a wide margin once a lift or four people are involved.
Questions people ask about mechanical takeoff software
Do these need trade-specific products?
The libraries help and the discipline is portable. A general takeoff tool plus your own assemblies works; what does not work is borrowing another trade's labour units and assuming they transfer.
Where do labour units come from?
Published references, manufacturer data or your own completed jobs. The third is the only one that reflects your crews, and firms that never compare the three keep bidding at somebody else's productivity.
What is most often under-counted?
Terminations, fittings, hangers and testing. The equipment is on the drawing and gets counted; the work of connecting it is implied and gets missed.