Several parts of that are tricky without knowing more about the business.
For install, is the goodwill with you, personally, or the business? The relevance of goodwill, and perhaps much of the growth trend, will depend on how much of it is you. If you sell on eBay, and customers won't be aware the owner has changed, the goodwill may be with the business. But if you sell via street stalls, car boots, trade shows etc, and the customers recognise you, personally, then the trust and recognition won't transfer.
As for equipment, suppose I were buying your business. I'm less interested in notional depreciation than what I could buy equipment to do the same job for now, elsewhere. Have prices, new or used, gone up or down? Or, if I buy new, it might cost more but would I get better tech, faster production, lower matetials cist or more varied and versatile hardware, etc.
For instance, if you bought a 3D printer 5 years ago for £10k (figures are spurious, not realistic) and depreciated it by 10% of balance, it'd be "worth" about £5900 now after 5 year's depreciation. But, as that was early tech, I can buy a better, faster, higher res machine handling more materials, and do it for £1500, then I'm not going to value your machine at cost less some notional depreciation of four times that amount. Depreciation is really just a notional bookeeping figure for mainly tax reasons, and the crunch comes with a balancing charge on scrapping or disposing of the machine, when you'll add or deduct accordingly.
How does the notional value, after depreciation, compare to you selling the equipment, as used, on the open market?
My final point is this. Suppose I'm a prospective buyer of your business. I come to you, you show me your operation, and the books. What will it cost me if I go away, buy the equipment piecemeal, new or used, and set up myself from scratch?
On the other hand, if the "value" of your business is that you've put a lot of time and effort into designs that you own, with IP rights, and those designs represent the value, then buying a 3D printer myself won't help me much without the design files.
On goodwill, if you have a lot of customers where a personal relationship exists, and you're prepared to work with a buyer for days or weeks, in a handover phase to keep those customers with the new owner by introducing and recommending, then the goodwill might be more valuable. If you're planning on sticking everything in a box, taking cash in one hand and giving the buyer the box with the other and showing him the door, then why should customers not simply go elsewhere?
Booyaka is right. Your business is worth what someone will pay for it. Your best best in working out what that might be is to work out exactly what it is they're buying, and what it's worth to them. If I was that buyer, what exactly is it in your business that represents something that, to me, is worth paying for. That, and your sales and negotiating skills, and the cost of me buying an equivalent elsewhere, will determine price.
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